Orchidaceae – a plant family with an extraordinary diversity of species.
Orchis, a genus of European Orchids, lent the name to the entire family.
God’s own flowers.
Welcome to the world of Orchids. The variety, rarity mysticism that surrounds the flower all contributes to the love, curiosity and love of people around the world.
Perennial plants which are members of the largest family of plants – Orchidaceae are known as Orchids. It is estimated that there are about 25,000 species of orchids in the wild. Relatively young age of the genus can be the reason for this astonishingly high number of species.
Loss of habitat has led to considerable decline of orchid population in the wild but fortunatly among plants Orchids in particular have become highly sought after flowers, gardeners and lay admirers cultivate them in greenhouses and households in cooler regions. And that remains the only possible way to sustain these fabulous plants. we here provide information on the various species of orchids.
The region designated as South India lies between 8 degree -20 degree north of the equator and between 70 degree -85 degree in longitude. The mean temperature is 27 degree C(81 degree F) at sea leavel which it enjoys with Northern Australia , New Guinea , Phillippines , Indonesia , Malaysia , Sri Lanka , Tropical and major part of South Africa , parts of Brazil, Guyana , Columbia ,Venezuela , Panama ,the Honduras and Guatemala . The southernmost regions of the peninsula lie on the northern fringes of the equatorial belt. The peninsula which extends north-south touching Indian Ocean at its southernmost tip , is flanked on the west by the Arabian Sea and on the East by the Bay of Bengal. On the north is the arid expanse of the Deccan plateau beyond which are the Vindhya ranges . Stretching parallel to the Western coastline and bout 40-50 miles inland are the mountain ranges of Sahyadri or the Western Ghats as they are more commonly known. This extends southwards from Bombay to nearly thirty miles short of Cape Comorin. Except for a gap, about 20 km wide somewhere midway between its two extremities , the Western Ghats are one unbroken stretch of mountainous terrain, rising imposingly from the coastal plains and gradually sloping off into the semiarid expanse of land towards east, and throwing up peaks of upto 2300 m at frequent intervals.
Lining the eastern coastline and lying parallel to the Western Ghats , but much less imposing and stopping short at the middle of the peninsula, are the Eastern Ghats.
Our present survey of orchid populations was mostly confined to the coastal state of Kerala and a few nearby areas in Tamil Nadu , which occupy the Southern regions of the peninsula . The combination of the geographical factors discussed above along with the yearly excursions of the sun towards the north and south of the equator , render these southern coastal regions exposed to both South West and North East monsoons . These monsoons drench the land for six moths of the year from June to November ,and provide sporadic showers during the remaining six months .
During the hot summer months of June and July the sun is at its northern zenith. The fierce vertical rays of the sun heat up the entire Central Asiatic region, which sets up a pressure gradient between this region and the comparatively cooler southern parts. As a result , air currents from the equatorial regions below over to the mainland Asia . These air currents , as they come sweeping over the vast expanse of the waters of the Indian Ocean, get saturated with water vapour, which they unload against the cool heights of the Western Ghats. This causes such heavy precipitation over the mountain ranges that this has became one of the wettest spots in the World. As much as 426 cm. of rain has been recorded in some of the southern parts of the Western Ghats. In these regions the greatest amount of precipitation is during the months of June and July , when the sky would be constantly overcast and it would go on raining for days at a stretch. The temperature at this time of the year may vary between 75-80 F at a day time and between 60- 75 degree F during night. The relative humidity is almost always at or near saturation point.
The fury of the south west monsoon is lessened to a considerable degree as it travels north. The costal of Goa , Karnataka and Maharahtra get less of precipitation than the southern regions.
During August and September the force of monsoon abates considerably During its fag end, the sun is once again at the equator ,ready to start its journey southwards. The whole course of events which has set in motion the onset of south-west monsoon , is now reversed . The comparatively cooler air from Central Asia and Himalayas blows to the now hot equatorial and southern regions . This north-east monsoon winds bring showers which the eastern slopes and regions east of the Western Ghats enjoy during the months of October and November . Since north-east monsoon winds travel mostly over land area before they enter South India , the showers these winds bring are far less heavy than those of south-west monsoon. During this season, south-western regions of Western Ghats experience a very predictable weather of bright sunny mornings and cloudy afternoons with thundershowers which may last well into the night.
The moths following north-east monsoon, from December to February ,when the sun is at its southern zenith, are comparatively dry with little or no rain. But during this time , temperature is low for a tropical region and nights are coolest of the year, the temperature dropping down to as low as 60 degree F on most nights.
The months of March , April and May are the hottest of the year, the temperature now soaring to 90-100 F during day-time and never dropping below 80 F at night . There are occasional showers to relieve the monotony of this summer heat.
The heavy rainfall contributed by the two monsoons and spread over six months of the year and the high temperature of the tropics , make the south-western coast of the peninsula , one of the most humid regions of the world. This situation is enhanced to a great degree by the proximity to the sea throughout its entire length . The tropical rain forests of Western Ghats are veriable orchid gardens and the great majority of orchid species reported from South India occur at elevations of 700 m and above in these mountain ranges.
The plants of western costal region include most of Kerala State, parts of Tamil Nadu, Karnataka , Goa and Maharashtra . Here the rainfall is high and there is a dense population of orchids. For a person motoring along the highways , particularly in Kerala ,the wayside avenue trees bearing huge masses of orchids would be a very common sight. But this population of the plains , even though large in number , comprises of only five or six of the more hardly species ,which are adapted to withstand the high temperature without damage to the foliage .
As mentioned earlier , the area east of Western Ghats receives only a nominal amount of rainfall and is mostly a tropical savannah towards south and an arid semidesert towards north. Both these regions have only a sparse orchid population because of the low degree of humidity and the high temperature . Amidst this expanse of arid plains , the Eastern Ghats, provide a sanctuary of sorts to orchids. But compared to Western Ghats , the amout of rainfall here is low and orchids of Eastern Ghats are mostly succulents or semi-succulents , adapted for existence in moisture-deficent areas. As a result of the efforts of Wight , Hooker , Fischer , Blatter & McCann Santapau and Kapadia ,nearly 240 species of orchids have been reported from South India . In later years stray reports of a few more species have also been added to this . Altogether there are under 250 species in about 70 genera reported from this region . Nearly 60 % of the species are epiphytic the remaining 40 % constituting the terrestrial flora. Habenaria and its allies form half of the terrestrial population , the other half being constituted by the various Neottieae , Malaxis, Liparis , Eulophis etc. Among the epiphytic forms there is a preponderance of sympodial forms.
No.of genera which are monotypic -37
Genera with number of species 2 –Calanthe, Sirhookera, Phaius , Gastrochilus , Acampe, Diplocentrum, Vanilla ,Zeuxine, Disperis , Porpax, etc.
Genera with number of species 3- Cymidium
“ 4-Nervilia, Vanda
“ 5- Luisia , Malaxis
“ 6- Saccolabium ,Aerides , Coelogyne
“ 9- Eulophia ,
“ 10 – Oberonia , Liparis , and above – Bulbophyllum , Dnedrobium ,Eria, Habenaria , Peirstlylus .
The largest genus among South Indian Orchids is Habenaria and among epiphytic species Dendrobium.
The orchid population of Western Ghats becomes especially interesting when we take into consideration its apparent isolation . The main orchid growing regions nearest to south India are separated from it by either vast expanses of water or by equally vast expanses of arid land mass. Tropical Africa and Madagascar on the West, the Indo-Burmese and South East Asiatic region on the North and East are effectively separated from South Indian orchid growing regions. The island of Sri Lanka ,which lies nearest to South India and has almost the same climatic conditions is , nevertheless, separated from it by the Gulf of Mannar.
Depending upon the influence of these neighbouring orchid growing regions , the orchid flora of South India may be divided into the following sections:
1. The endemic element
2. The Ceylonese element
3. The Himalayan and South East Asiatic element..
1. The endemic element
Of the 240 species , 102 are endemic to South India .But rather surprisingly , none of the 64 genera are endemic. Two genera, Cottonia and Sirhookera are exclusive to South India and Sri Lanka. All species of Bulbophyllum , and Eria and more than half of the larger genera like Dendrobium and Habenaria are endemic .
2.The Ceylonese element
Hooker reported 180 species of orchids from Ceylon (Now Sri Lanka). As in the case of the South Indian species, the orchid flora of Sri Lanka also maintains a considerable amount of individuality , as is evidenced by the 104 species , which are endemic to the island. There are only 37 species which South India and Sri Lanka share together . It is surprising that these two geographically juxtaposed regions, separated by a narrow stretch of water ,should maintain such a high degree of individuality .
2. The Himalayan and South East Asiatic element
The greatest of outside influences on orchid flora of South India appears to be that of Himalayan region . About 68 of the species found here are native of the cool Himalayas . Twently –three of these extend also to Burma and 15 to Malaysia and possibly to Thailand also.
Besides these individual influences , there are some 30 species which are found to occur in all three of the above regions.
Though Africa is as much of a neighbour to South India as Malaysia and Thailand are ,yet the African influence on South Indian orchid population is only at the generic and never at the specific level. Flora of both places are typically of the Old World with such genera as Habenaria , Disperis ,Satyrium, Bulbophyllum , Eulophia ,Acampe, Vanilla, Nervilia , Liparis , oberonia etc. But no species are reported from both places so far, even though there is very close resemblance between certain species which occur in East Africa and Sounth India ,eg. Calanthe volkensii and Calanthe masuca , Eulophia schimpeiana and Eulophia epidendraea etc.
Occurrence of the same species in different parts of the same continent is usually explained by long range dispersal . Species like Dendrobium crepidatum and thrixspermum arachnites, which are of common occurrence in Himalayan and South East Asiatic regions , but are of comparatively rare and localized distribution in South India , may have come to occupy the latter terrain through human agency , or better still , through the agency of migrating birds. This may very well be the case with the thirty odd species which south India shares with Sri Lanka.
We have to seek explanation elsewhere for the similarities between South Indian and African flora . As pointed out earlier ,the relationships are at the generic rather than at the specific level. This naturally points to common ancestors in the distant past and subsequent divergent evolution in Asiatic and African continents. Such a situation can best be explained by the theory of continental disjunction as propounded by wegener during the early part of this century . According to this theory , earth’s land surface was one solid mass before Pleistocene; it split up into continents which slowly drifted away to occupy their present positions later on . The main evidence in favour of this theory is the shape of the present continents ,which if put together ,will fit like the pieces of a jig-saw puzzle. In this united condition the present peninsular India may have remained appressed to the South East African Coast on one side and the South East Asiatic countries on the other . During this time they might have possessed many plants in common. After disjunction , due to climatic changes which might have happened in the case of each continent ,divergent evolution might have taken place giving rise to the different yet related population that we see now.
Types of orchid population in South Inida
The vegetation on the Western Ghats in general is constituted by what is typically designated as tropical rain forests . But depending upon the amount of rainfall ,there may be differences in the type and amount of vegetative growth in different parts of the mountain range. As was explained earlier in this chapter , the western slopes of western Ghats receive for heavier precipitation than any other part, which are naturally considered as rain-shadow areas, where the orchid vegetation is mostly composed of succulent species like Luisia ,Diplocentrum, Oberonia etc. , and hardly forms like Vanda spathulata ,V. tessellate and V. testacea.
Sea level -300 m
The Western coastal plains,due to its heavy annual rainfall and the juxtaposition to the sea along its entire length, retains a high amount of moisture in the atmosphere . but temperature is too high for most species of orchids. The 5-6 species which survive this temperature ,however, thrive and proliferate to such an extent that practically every tree is covered by one or more of these species .Acampe praemorsa, Dendrobium macrostachyum , Luisia zeylanica, Pholidota pallida, Cymbidium aloifolium, Bulbophyllum neilgherrense are the species which are found in the plains. There is only one terrestrial orchid which occurs commonly at sea leavel-Eulophia epidendraea.
As we get nearer to the mountain ranges the density of orchid population increases . Species like Rhynchostylis retusa ,some Oberonias , Vanda testacea appear on the trees. Malaxis versicolor ,Geodorum densiflorum are found among terrestrial forms .
As we go up the mountain ranges ,the forest thickens and temperature falls at the rate of 1 degree F for every 95m. Oberonia brunoniana ,Dendrobium ovatum, Polystachya flavescens, and Aerides ringens appear and intermingle with the previously mentioned species , which gradually disappear.
This is the region of the typical rain forest . Huge trees, often more than 30 m. in height, form a thick canopy of leaves, through which little light penetrates. Undergrowth is reduced to a minimum. Calanthe masuca , Acanthephippium bicolor, Eulophia macrostachya , etc. , grow on the forest floor, in the dense shade while species of Malaxis and Liparis occupy regions nearer to grasslands ,where light penetration is high. Epiphytic species are rare due to the scanty light penetration. Those species which require perpetual moist conditions such as Dendrobium heyneanum ,various Eria species with discoid pseudo-bulbs , Cymbidium pendulum, Gastrochilus pulchellus etc., are the main occupants of tree trunks . A few species which require plenty of sunlight such as Eria pauciflora, Malleola gracilis etc., also are found at this altitude, but always occupying the topmost branches of the trees, so that no amount of sunlight is missed .
The rain forests thin out . The fall sparsely branched trees of the tropical rain forests give way to small , stunted trees with spreading branches . Wide expanses of grassaland appear in between clusters of trees. Gallery forests, i. e., encroachments of forestlands into grassland along temporary stream beds or park savannahs , i. e.,grasslands with scattered clusters of trees here and there are a min feature of the mountain ranges of this altitude. Actual rain fall in this area may be lower than in the rain forests , but there is always a nightly mist which more than compensates for the diminished rainfall . Plenty of sunshine is available and free air circulation is possible . This is the ideal orchid country and here we find the majority of orchid species which are epiphytic , thriving luxuriously on the stunted trees. Dendrobium heterocarpum ,Dendrobium nutans ,D. microbulbon, D. nanum, the various Cirrhopetalums , etc. , reach their maximum growth here. The various terrestrial tuberous forms like Habenaria , Peristylus , Pecteilis etc., Eulophia nuda,E. cullenii etc. also thrive in the grasslands , in full sunshine.
Mostly savannahs . Here it is too cold and dry for epiphytic species. Except for a few species of Coelogynes, Cirrhopetalums and Aerides maculosum ,not much of epiphytic species is seen. Habenaria and its allies continue to occupy the meadows though at a diminished frequency.
2300 m and above
No epiphytes. Even the terrestrials vanish .
Flowering in orchids
In nature the majority of orchid species flower only once a year. The flowering time may vary according to species and the climatic conditions of the area occupied by the species . So much so , there is no particular time of the year which can be quoted as the flowering time for orchids in general. But there are particular times of the year when a large number of orchids come into bloom all at once. As far as the South Indian species of orchids are concerned , there are two such peak periods in flowering time .
1. Immediately after the great force of the monsoon has abated , during the months of August and September, most of the terrestrial forms like Habenaria and its allies , Liparis , Malaxis etc., come into bloom. They send up aerial shoots with the first rain,which grow up rapidly during the two months of heaviest rainfall , produce flowers during August and September and by the time rain abates the aerial portions die down leaving the tuber to remain underground till next year. There are also several epiphytic orchids which burst into bloom with the first rains,e.g., Rhynchostylis retusa, Aerides ringens, Eria pauciflora , Bulbophyllym fischeri, Bulbophyllum kaitense , few of the Oberonias, Ceologyne mossiae, C. nervo, Aerides crispum, A. maculosum etc. Altogether more than 60 species of orchids flower during these months in South India .
3. The second peak in flowering affects mostly epiphytic species , and occurs during the months of March and April. This second gregarious flowering may be in response to the increase in temperature and sunlight experienced by the orchids in the wild . During summer months there is some amount of shedding of leaves by the trees even in evergreen forests as a protective measure against excessive transpiration through leaves. This increases the amount of sunlight falling in these species . Acampe praemorsa, Bulbophyllum firmbriatum , Bulbophyllym tremulum , Dendrobium herbaceum D. crepidatum ,various Luisia species , Vanda testacea ,Coelogyne odoratissima C. glandulosa , Trichoglottis tenera etc. are some of the species which come into bloom at this time of the year. Among terrestrial species Eulophia macrostachya , Acanthephippium bicolor, Eulophia nuda also flower at this time.
There are a few species of South Indian orchids which bloom in response to the cool nights of January and February ,e.g., Dendrobium heterocarpum , Bulbophyllum aureum , Chiloschista pusilla etc. Most of Neottieae , like Zeuxine , Anoectochilus , Goodyera , Cheirostylis etc., come into flower during this time .
Species like Dendrobium haemoglossum , Thrixspermum arachnites , Ephemerantha macraei etc ., flower periodically . In the case of the Malaysian species ,Dendrobium crumenatum , it has been reported that a sudden drop in temperature of 10 F will induce flower bud initiation .This may also be the case in the above mentioned species as well. In all these cases flowers last only for a brief period , a day or two.
As in any other orchid population anywhere else in the world , here also there are species which find conditions existing in South India conducive for growth and reproduction , as well as species which just manage to survive in a few localities . Most of the hardy species occur in the plains and these are the most prolific of the lot,eg., Acampe wightiana, Dendrobium macrostachyum, Pholidota pallida etc. Among species which thrive on hilly ranges at low elevations , Aerides ringens , Rhynchostylis retusa , Polystachya flavescens etc., are the commonest . In the rain-shadow areas , Vanda tessellate and Vanda testacea are the most common species .
Variations in morphological aspects of the same species existing in different localities and different altitudes are great . An interesting example is provided by Aerides ringens which occurs with slight variations from 300 m above sea leavel to 2000 m . At 300-600m this plant usually has thick dark green leaves heavily mottled with purple and profusely branched panicles with white flowers having the faintest touch of pink . At elevations of 800-1200 m the plants have paler and wider leaves. The main axis of the inflorescence grows horizontally from which upright branches are given off . Flowers are larger and fewer in number and pink in colour . Higher up between 1300 – 1700 m the leaves are again dark green and mottled with purple , but inflorescences are seldom branched and flowers are a bright magenta in colour .
Among terrestrial orchids , Calanthe masuca , Geodorum densiflorum , Eulophia macrostachya , Acanthephippium bicolor etc., are the most widely distributed . In the higher altitudes Dendrobium herbaceum , Eria polystachya , Eria pauciflora are the most abundantly and widely distributed species. Species like Dendrobium heterocarpum ,D. nutans ,D. heyneanum , Trias stocksii etc., are widely distributed but few in number in each locality , whereas Bulbophyllum aureum , Phalaenopsis decumbens , Thrixspermum arachnites , Rhynchostylis latifolia , Phaius luridus were indeed scarce occurring in one or two localities .
Habitat destruction is the most effective form of removal of any particular form of life from the face of earth. As far as the South Indian orchids are concerned , destruction of natural forests is the greatest threat to their existence. During the mad plunder of the Himalayan orchids during the pre-independence days, the orchids of South India escaped a similar fate, because they were not as showy as their ill-fated Himalayan counterparts and also because this stretch of orchid-growing land is rather isolated from the other parts. There is also probably a third reason, which is that the people of South India are not yet quite aware of the wealth of orchids their mountains possess, nor have they realized what these plants are worth in the foreign market. So long as this state of affairs prevails , there will be no threat of overcollection for South Indian orchids.
But ever since the various plantation crops were introduced here and especially during the past two decades , there has been an unprecedented amount of clearing or forest land for purposes of agriculture . This has been true particularly in the State of Kerala where the Government has recently passed regulations to take over all privately owned forest lands. The land owners, in order to retain land , went into a fenzy of converting forest lands into plantations ,with the result that acres of orchid-inhabiting areas were destroyed . Fortunately not all kinds of forest clearing affects natural orchid population ,eg. , the cardamom plantations usually need heavy shading and there is need for only selective felling of trees , before the land is prepared for planting . This usually involves a clearing of the undergrowth ,while the tall trees are left as they are . Orchids are benefited rather than harmed by such selective felling . The free air movement and the increase in sunlight provided by the clearing away of several crowded trees and the undergrowth in an otherwise dense tropical rain forest , encourage growth of epiphytic orchids. This fact was evident in many of the cardamom plantations we visited during our survey . Rather unfortunately not all plantation crops need heavy shading .
Even in forest areas which have been left unmolested by the above agencies ,threats to the peaceful existence of orchids occur in one form or other . The people who eke out a living by selling the natural produces of the forests like honey, cane , etc., are the main agents of destruction here. In the dry summer months , in order to make their forest trails clear and to keep away reptiles etc., are the main agents of destruction here . In the dry summer months , in order to make their forest trails clear and to keep away reptiles etc.,they set fire to the dry grass. This fire may destroy not only the grass , but also the various terrestrial orchids that grow among the grass, particularly those which do not possess underground tubers . It has been suggested that this may be the reason why the much sought after Paphiopedilum druril,which according to Col. Druru were growing abundantly at the top of the Calcad Hills at one time is now practically extinct .
It is indeed a consoling fact to those who love orchids, that moves are being made at international level for the conservation of orchids . The American Orchid Society has formed an Orchid Conservation Committee with W.W.G. Moir as Chairman and six others as members . The international Union for the Conversation of Nature and Natural Resources has a Survival Service Commision functioning under it . This Commision also has a pilot scheme for spotting and conserving endangered species .
Saving of endangered species is only one half of the picture . Only by providing proper sanctuaries to these species can their safe future survival be assured . Just as we provide sanctuaries for wild animals and birds , so should proper habitats be provided for the orchid species as well , so that the infinite variety and colour which these unusual group of plants contribute these lines in India is now being initiated under the leadership of the Director of the Botanical Survey of India .
As in their vegetative habits , in flower size , shape and colour also , the orchids exhibit a wide range of variations. As Lindley remarked ,”……..flowers are produced so unusual and so grotesque in form that it is no longer with the vegetable kingdom that they can be compared , but we are forced to seek resemblances in the animal world .” In most cases flowers are smallish , to seek resemblances in the animal world.” In most cases flowers are smallish , but the range of size may vary from that of some species of Oberonia where it is only 0. 15 cm. Across to Pecteilis susannae which may be as much as 10 cm . across. Platystele ornate of Venezuela has flowers which are smaller than a pin-head . The predominant shades are white , yellow , green and purple seen in the pure state or occurring in every conceivable combination . The beautiful azure blue of species like Vanda coerulea , valued among orchid breeders occur among South Indian orchids only in the lip of Vanda tessellate . So also is the bright orange red which made species like Ascocentrum ampullaceum very popular among orchids lovers , seen only in the lip of Vanda tessellata. So also is the bright orange red which made species like Ascocentrum ampullaceum very popular among orchid lovers, seen only in the pendant species of Schoenorchis filiformis which , in spite of its smallish flowers , looks very dainty and elegant .
Notwithstanding this great range of variety in form ,the general structure of the flower in orchid is remarkably uniform . Except in a few cases like Malaxis, Oberonia , Satyrium , etc., the flower , as it appears to us , is in an upside down position , having through 180 degree on its pedicel.
The three outermost segments or sepals are most often similar or at least subsimilar in appearance , the laterals sometimes becoming falcate. But in a few cases like some Bulbophyllums , Renanthera, many Oncidiums etc., the odd sepal is of a different size from the laterals. In species of Porpax, Cryptochilus, Masdevallia etc., the sepals unite into a tube with only the ends free of each other . In Paphiopedilum , Cypripedium , Rodriguezia etc., the lateral sepals cohere along their entire length . In the tropical American Cryptochilus , Masdevallia etc. , the sepals unite into a tube with only the ends free of each other . In Paphiopedilum , Cypripedium , Rodriguezia etc., the lateral sepals cohere along their entire length. In the tropical American Cryptophoranthes these fused lateral sepals also unite with the odd sepal at the base and the tip, leaving the middle portion free, so that the flower never opens . This peculiar construction has gained for this orchid the name window orchid. In Fabenaria perrottetiana, Brachycorythis etc. the odd sepal unites with the petals to form a hood over the column.
The petals are , as a rule, much more brightly coloured than the sepals. Of the three segments , the odd one is modified into the labellum or the lip , which , in most cases , is larger , three-lobed and more brightly coloured than the laterals . The petals may be similar to the sepals in size, but in a few cases as in some Habenaria and Coelogyne species of the old genus Cirrhopetalum they are much smaller than the sepals . In Lichenora , Cryptochilus , Masdevallia etc. they are hidden by the sepaline tube. But in Cypripedium sanderianum , C. caudatum ,C. caricinum etc., they are very conspicuous by their twisted ribbon-like form and several inches of length.
The labellum is the most prominent of all perianth parts , being endowec with arresting colours , unusual forms and peculiar markings , ridges and grooves . Except in a few instances like Bulbophyllum , Eria etc. the lip is trilobed , with the central lobe much more prominent than the side lobes . In Dendrobium brymerianum and Brassavola digbyana the fimbriation of the lip attains extreme proportions . Odontoglossum and Miltonia show very peculiar markings on their lip. In the latter, perfect reproductions of common numerals are sometimes seen, imprinted in contrasting colours .
The lip is attached to the base of the column. The mode of attachment may be rigid of loose. In the South Indian Bulbophyllum tremulum and the East African B. distons , the lip is provided by several movable hairs, which catch even the slightest movement of the wind.
But the most fascinating aspect of the lip is its habit of mimicry . More often than not , this serves to promote pollination by insects . In such cases , the lip is modeled as an exact replica of the female of the insect-pollinator . The Mediterranean wasp orchid has a lip which resembles a female wasp and emits a similar odour, and is believed to attract the male. But what is even more remarkable than these are the instances where the lip gives the unmistakable impression of comic imitations of distinct animal forms. Such pranks appear to serve no purpose at all, except perhaps, to add to the element of the unusual which already is part of orchid architecture .
The orchid flower may or may not be spurred . This appendage of the lip is meant for storing nectar and is possessed by quite a number of species . It may vary in shape and length in the different species. In the African Angraecum sesquipedale, it reaches a length of one foot. In many Peristylus species , it is scroriform or globular , whereas in Gastrochilus , it is wide and cup-shaped . There are two spurs instead of one in satyrium and diplocentrum.
Situated in the centre of the flower opposite the lip and facing it is the unique structure ,the column or the gynostegium ,which is peculiar to the orchids and their chief identifying character. The gynostegium is formed by the fusion of the filaments ,styles and stigmas of the flower . The only fertile anther of the flower is borne on top of the column. In diandrae , where two anthers are fertile , they are borne subteminally on the two sides of the column . In orchideae and Neottieae ,the anther is persistent ,whereas in the advanced Epidendreae they are deciduous . The anther cap which is easily removable in the deciduous forms , provides a protective covering over the pollen grains, which are collocted in masses called the pollinia . The pollinia are contained in a cavity called the clinandrium . There is a great amount of variation in the construction of the pollen apparatus in the various species. In the primitive Diandrae pollinia are not formed ; instead pollen grains adhere together by a viscous substance. In Neottieae and Orchideae pollinia are organized but are of soft consistency. In the former they separate easily into a powdery mass and are termed granular of mealy pollinia are organized but are of soft consistency . In the former they separate easily into a powdery mass and are termed granular or mealy pollinia while in the latter they cohere in packets and are termed sectile pollinia . In the advanced Epidendreae the pollinia are hard and waxy .
The pollinia may or may not have appendages . In Neottieae and Orchideae and advanced subtribes of Epidendreae , like Oncidiinae and Sarcanthinae , these appendages are present and the whole structure is called the pollen apparatus , being consistuted by the pollinia , the stipe and viscidium to caudicle , which is a tail-like prolongation of the pollinia . The stipe is of columnar derivation and is often hygrophilous . The caudicle and disc are part of the pollinial apparatus in Orchideae also . But here they are derived from the pollinium itself and are thereby morphologically distinct from the stipe and disc of the Sarcanthinae.
In the primitive subtribes of the Epidendreae pollinia are prolonged into a tail as is seen in Calanthe , Eria etc. In Cattleya the pollinia are lenticular and have a distinct ribbon-shaped appendage which lie inside the clinandrium and is called as ‘ appendicula’ by Bentham.
The number of pollinia may vary from 2,4 and 6 to 8 . Six pollinia are of rare occurrence and are found only in a few genera like Hexadesmia , Leptotes, Tetramicra etc.
In Orchideae the various packets of pollinia are drawn together by elastic threads into one club-shaped mass with a stalk-like caudicle ending in a disc. The pollinia , two in number , lie one in each half of the anther which is made up of two erect bag-like containers or loculi. The disc is kept hidden in a flap of brusicle and is always moist with the secretion of a sticky substance . The pollinia cab be dragged out of their containers , which is what insects do unknowingly , during visits to the flowers.
Just beneath the anther is the rostellum which is morphologically one of the three stigmas modified . It extends a s a horizontal beaked plate between the anther and the functional stigma and it serves the purpose of preventing the pollen from failing on the stigma of the same flower . It is also supposed to secrete a viscid substance which holds the pollinia till it is mature to be disbursed . The viscid portion then dries up and releases the pollinia
On the ventral side of the column, beneath the rostellum is a hollow cavity which is the functional stigma of the flower . Actually it is the two fertile stigmas of the flower fused together . It is covered by a viscous substance which is very dear to the insects . This substance helps to hold the pollinia which are depostited on it during the process of pollination. For the same purpose , the stigma may also develop papillae on its surface . In species of Habenaria , stigmatic lobes are in the form of club-shaped processes projecting beneath the anther . Here when cross pollination fails , the pollen falls on the stigma and self pollination takes place.
In many of the Oncidiums , the column extends beyond the anther giving rise to cucullate of hooded anthers. In Catasetum the column has two extremely sensitive , bristle-like appendages below the stigma, which aid in releasing the pollen on to the insect’s back during pollination.
In genera like Eria , Dendrobium , Bulbophyllum , etc. and some genera of the Vanda tribe, the column is extended below beyond its attachment to the stalk of the flower , into a structure called the foot ,and together they form a sac-like ‘mentum’ which is characteristic of the above genera .
The ovary in Orchidaceae is generally tricarpellary , one-called , with three pariental placentations and innumerable number of ovules. In the primitive Apostasieae and Selenipedium of Cypripedieae , ovary is three celled with axile placentations.
Vanda and Phalaenopsis are especially susceptible to this disease . Cattleya and other genera are also affected . This disease is caused by Phytophthora omnovora , which is related to the potato wilt fungus . The disease starts in the interior of the plant and spreads to the leaves ,which turn yellow and drop off. If cut across ,the bulb will show dark rotted areas inside . Cut away infected bulbs , dip the plant in fungicide and repot in fresh medium.
Leaves in orchids conform to the usual monocotyledonous pattern . In terrestrial forms, it is either long and plicate , or short , elliptic oblong or linear ovate , but always with sheathing bases . In rare cases like Habenaria crassifolia , Nervilia etc. leaves may be orbicular . The jewel orchids Anoectochilus , Haemaria etc., have velvety leaves with silver or golden veins providing beautiful ornamentations .
In epiphytic species ,leaves like are thick and coriaceous , intended to prevent high water loss. In many of the evergreen species , they serve the purpose of storage organs as in terete-leaved Vandas, Diplocentrum , Saccolabium filiforme , Aerides cylindircum etc. In Cymbidium , leaves are long , linear and ensiform , often reaching a length of half a metre . In Oberonia and Podochilus , leaves are laterally compressed and succulent . In Chiloschista and Taeniophyllum , they are much reduced in size and are deciduous . Here the stem is also greatly reduced from which thick succulent green roots spread like the tentacles of an octopus in all directions . These roots take up the function of the leaves , synthesizing starch by photosynthesis .
The orchid seed consists of an undifferentiated embryo enclosed in a transparent air- filled seed- coat , which has cells devoid of protoplasm in the mature state . A highly sculptured sclerotic and opaque seed -coat is seen in the primitive forms like Apostasieae , Selenipedium and Vanilla .
According to Dressler and Dodson , relationships between tribes in Orchidaceae are as hazy as the affinities within are clear. Extinction might have occurred at this level this obscuring the interconnecting webs . On the basis of the primitive and advanced characters as exhibited by the living species of orchids which are discussed in the previous pages , all orchidologists agree that Apostasieae are the most primitive of all existing orchids and genera like Neuwiedia provide a connecting link between Orchidaceae and the other monocotyledons with trimerous liliaceous pattern of flowers like Hypoxis and Curculigo. It is suggested that from this Neuwiedia -like ancestor , with fertile anthers present in both the whorls, Cypripedieae might have evolved by the suppression of the outer whorl and the rest of the orchids by the suppression of the inner whorl of anthers .
In evolutionary status , Cypripedieae come nearest to Apostasieae . Diandrous condition , substigmatic insertion of the anthers , free pollen , tricarpellary ovary with axile placentation etc. are characters which bind the two groups together as the most priomitive tribes of orchids . But in the gross morphological appearance ,the Cypripediae appear more related to the monandrous orchids than to Apostasieae . Therefore , it is generally assumed that Cypripediae are not direct descendants of Apostasieae .
These two groups , Apostasieae and Cypripedieae have been variously treated by various authors . Some did not consider them as orchids at all , for example, Pfitzer , Schletcher and Mansfeld . Others went so far as to include them in the family but kept them as a distinct tribe on a par with Orchideae , Epidendreae etc. Holttum and Dressler and Dodson separated Apostasieae and Cypripedieae into a separate sub-family on the basis of their pleuriandrous condition . Bentham and Hooker went to the other extreme and included the genera Apostasia and Neuwiedia along with Cypripedium under the same tribe suggest that the Apostasieae be treated as a distinct tribe nearest in status to Cypripedieae on the one hand and NEottieae on the other .
The assemblage of primitive characters as well as the worldwide and sparse distribution of the four genera of Cypripedieae , justify the belief that they might have existed at a time prior to the origin of the monodrous orchids. Many of the living representatives of this group today exist in secluded and almost inaccessible regions , which are themselves isolated from each other by hundreds of miles of land or sea or both . Breiger (1960) has pointed out that the great continental disjunction separated genera in Cypripedieae , whereas in the monandrous orchids, groups were separated. This clearly shows that geographically Cypripedieae are more ancient than the monandrous orchids.
Although morphological appearances warrant a closer reltationship between Cypripedieae and monandrous orchids than between the former and Apostasieae , a direst line of descent from Cypripedieae to Monandrae is a possibility ruled out by all orchidologists . The main reason is the radical difference in the structure of the flower between the two groups . As mentioned earlier ,two different staminal cirlces are functional in the two groups. The fertile stamen of the monandrous orchids is the odd one of the outer whorl which is generally accepted patterns of evolution that the staminode of Cypripedieae should turn fertile to give rise to the monandrous orchids . The difference in the size of the chromosomes also support this argument. When compared to the other tribes of Orchidaceae , a particularly interesting point regarding the chromosomes of the Cypripedieae , is their remarkable size . The chromosomes of Paphiopedilum spiceranum range in length from 2.5 to 10 and are disproportionately large when compared to such genera as Eulophia and Geodorum , where they are only 1- 1.5 . For these reasons Cypripedieae cannot be considered as the direct progenitors of the monandrous orchids. It is true that Selenipedium has resemblances with Apostasia on the one hand and Cephalanthera on the other . But the best we can deduce is that the Cypripedieae and the monandrous orchids evolved from some remote ancestor along two distinct and separate lines. As Darwin (1877) remarked ” an enormous amount of extinction might have swept away a multitude of intermediate forms and left this single genus (Cypripedium ) as a record of the former and more simple state of the great Orchidean order ” . The fact that many of the living species of this group are now on the verge of extinction prove the validity of this assumption . Both in vegetative and floral characters Cypripedieae are unadapted for survival . They do not have either underground tubers or pseudobulbs to tide over unfavourable conditions. Their floral structure is such that self fertilisation is difficult to take place , in case cross fertilisation fails. It is seldom that a plant of this group is seen in the wild bearing pods.
As to which group of monandrous orchids comes nearest to this so-called common ancestral stock, which is supposed to have also given rise to Cypripedieae at a much earlier geological age , there is a great deal of speculation . Both in Neottieae and Orchideae aer comprised of comparatively primitive orchids. Orchideae , like Cypripedieae , are recognised as a specialised offshoot from the ancestral stock . They are characterised by the possession of two sectile pollinia each of which has a caudicle and a viscidium and is enclosed within an antherbag . The viscidium here , however , is morphologically rostellum. Outside Orchideae , sectile pollinia are seen only in the subtribe Spiranthinae of Neottieae . This could point to a relationship , but there are differences in the basic structure of the anther between Orchideae and Spiranthinae . In Orchideae ,the anther is erect and persistent , whereas in Spiranthinae it is incumbent and opercular. Dressler and Dodson are of opinion that Orchideae would have been quite isolated if it is not for the tow genera Epipogium and Stereosandra . Here the pollinia are sectile and anther persistent as in the Orchideae . In Epipogium aphyllum , the anther is incumbent as in Epidendreae , but E. roseum and Sterosandra have erect anthers. The earlier authors like Hooker and Schletcher treated these two genera as part of the tribe Neottieae . But Dressler and Dodson have put them under Orchideae threating them as connecting links between Orchideae and the rest of the orchids. They further venture to assume that Orchideae might have originated from ancestors closely akin to Cephalanthera .
Taxonomically the tribe Neotieae had a rather chequered history . The earlier taxonomists considered the group as nearly well defined . Dorsifixed anthers separated them from Orchideae where the anther was basifixed and mealy or granular pollinia separated them from Epidendreae ,where the pollinia were waxy . But later trends of thought put considerably less value on single characters , preferring the sum total of all characters i deciding reationships . According to Mansfeld (1937) , the subtribe Arethusinae of Neottieae has mealy pollinia but their relationships are more with Bletiinae of Epidendreae than with other subtribes of Neottieae . Accodingly he transfeffed this subtribe to Epidendreae . Besides , further knowledge on the morphology of the various genera revealed that what were considered as key characters till then , were not reliable enough to be made the basis of tribal delineations. Mansfeld (1937) has recorded the occurrence of mealy pollinia in certain genera of Bletiinae of Epidendreae , while waxy pollinia are seen in Sobraliinae of Neottieae. Naturally he transferred Sobraliinae also to Epidendreae . Dressler and Dodson went further and transferred three more subtribes , Pogoniinae , Vanillinae and Gastrodiinae , to Epidendrae , arguing that the affinities of these three subtribes are more with Epiidendreae than with the rest of the Neottieae a more natural group . But ,while these suggestions helped to break down the boundaries between tribes which were once well defined and firm , it still left the rest of Neottieae a very heterogeneous collection of subtribes ,which are not mutually as closely knit as those of Orchideae or Epidendreae.
Of the 9 subtribes recognised under Neottieae, Limodorinae with Cephalanthera , Epipactis and Limodorum ,are the more generalised and consequently the most primitive of all monandrous orchids. The genus Cephalanthera comes nearest to the probable ancestral group and provides connecting links with Apostasieae , Cypripedieae and Orchideae . The chromosomes of Cephalanthera and Epipactis and those of the related Neottiinae are the largest of all monandrous orchids and remind one of the situation in Cypripedieae .
We do not know anything about the cytology of Chloraeinae , Rhizanthellinae , Prasophyllinae etc. Isolated in the continent of Australia ,the genera included in these subtribes have undergone considerable development by way of specialisation .
Spiranthinae is a very distinct group , but with doubtful affinities . Dressler and Dodson are of opinion that they could be raised to the status of a tribe because of their isolation . The lowest chromosome number reported so far from all Orchidaceae is , from this group (Zeuxine – n = 10 ) .
If Neottieae represents a particualr state in the several evolutionary lines which fed into the vast and diverse tribe Epidendreae, as is often postulated, then there is no validity for its existence as a tribe , because in a taxonomic system based on phylogenetic principles , grouping together of genera on the basis of a character which represents only particular phase through which the family has passed in its evolutionary history , is not warranted . A great deal of further work is necessary for understanding the relationships of Neottieae . Here there are further complications . This is a primitive tribe and as such , extinction might have created large voids , thus obscuring relationships further .
The tribe Epidendreae is the largest in Orchidaceae and includes the advanced forms with waxy pollinia . Hooker treated this group under two tribes Epidendreae and Vandeae , the division being based on absence and presence of appendages to the pollinial aparatus .Pfitzer , Schletcher , Mansfeld and Dressler and Dodson considered them as one section , but the first three authors proceeded to divide it into further subsections . Pfitzer and Schletcher divided it into three sub-sections . Acranthae , Sympodiales and Monopodiales ; Mansfed followed Hooker and divided the section into Epidendreae and Vandeae , but Dressler and Dodson postponed such subdivisions to a future date, expecting that as more information accumulated they will provide clues to several of the missing links . They treat the genera included under this tribe directly under 27 sub-tribes .
Epidendreae is a vast and diverse group and is considered to be polyphyletic in origin . But the chromosome numbers in the tribe show a remarkable degree of uniformity . Out of the nearly 800 species investigated so far, about 53 % have 19 and nearly 40 % have 20 as their haploid number . But this uniformity evident in the number of chromosomes , does not extend to the morphology or size of the chromosomes . For example ,the genus Calanthe and Epidendrum have 20 aa the haploid number . But in Calanthe , the chromosomes are as long as 5 in length , while in Epidendrum , they range in length between 0.8 – 1.5 . It is to be assumed that these two genera ,though possessing the same number of chromosomes , neverthless , are representatives of two distinct lines of development within Epidendreae . On the other hand , other 20- chromosomed group like Coelogyninae and Cymbidiinae do possess chromosomes which resemble those of Calanthe in all morphological aspects . Here we can indeed speak of an affinity ,which is further emphasized by the same geographical distribution .
The differentiation into species of the Eastern and Western world is far more pronounced in the epiphytic rather than in the terrestrial species . The tropical Asiatic representatives of Epidendreae constitute a section very distinct in development from their occidental relatives . The two great Eastern tropical groups are the Dendrobiinae and the Sarcanthinae . As mentioned earlier, there are remarkable similarities in number , size and morphology of chromosomes between these two groups . In both , the chromosomes measure between 1 and 3 in length and 19 is the prevalent haploid number through 20 is also reported in a few species of Dendrobium and in a lesser of species in Sarcanthinae . Sarcanthinae are considered to be the most advanced group orchids of the Eastern world ,because of their monopodial growth pattern and possess naked pollinia without appendages . This type of pollinia are supposed to be primitive and accordingly Dendrobiinae have been allotted a low position among sympodial forms. But Holttum (1964) has suggested that this naked condition of the pollinia could be achieved through loss of appendages which at one time the group might have possessed in its evolutionary history . On the other hand Dressler and Dodson have suggested that limitations in the range of floral variations seen in Dendrobium are the result of their naked pollinia , which has seriously hampered the progress of evolution in this subtribe . Sarcanthinae have escaped this sort of stagnation , because of the complexity of their pollinial apparatus ,which enabled them to have wide range of floral variation . This has occured also in subtribes like Genyorchidnae which are closely related to Dendrobiinae . It is alos probable that both Dendrobiinae and Sarcanthinae might have achieved the 19-chromosomed condition independently . It would be interesting to assess the cross-compatibility between these two major groups.
According to Holttum , sympodial forms that come nearest to the monopodial types are species like Dipodium and Grammatophyllum . This does not mean that the monopodial species have evolved from these two species . On the othere hand, this change must have occurred in more than one line of descent . Dipodium and Grammatophyllum might represent relics of such forms which monopodial forms might have originated . These two genera have elongate stems , lateral inflorescences and pollinia with stipe as in monopodial species. Dipodium pictum is even monopodial in growth .
Discussing the various evolutionary trends within Sarcanthinae group of orchids, Holttum suggests that types like strap-leaved Vanda are the most generalised in this subtribe and thus represent the central primitive figure , from which other types seen in the group might have evolved . Vandas are large plants with coriaceous leaves at moderately spaced nodes , large flowers which are long -lasting with no complicated appendages on the lip and with two progress in evolution which is aparent in such genera as Saccolabium and culminates in such specialised forms as Taeniophyllum , where the leaves are reduced to scales and epiphytic roots with chloroplasts take up the function of leaves. With the reduction in size flowers are short-lived , and the lip gets more complicated with warts , and other appendages . Commensurate with this there is advancement from the two notched pollinia of Vanda to four pollinia in two pairs as is seen in Arachnis and Renanthera , from there to four equal pollinia as in Taeniophyllum and Microsaccus and finally to two undivided pollinia as in Taeniophyllum and Microsaccus and finally to two undivided pollinia as is seen in Saccolabium , Chroniodium , Microtachorchis , Hymenorchis etc. The state of two undivided pollinia may also be achieved by the elimination of the notch from the Vanda type .
The tropical American representatives of Epidendreae form two main lines of development , one represented by the comparatively primitive Epidendrinae and the other constituted by the relatively advanced Maxillariinae ad Oncidiinae . In Epidendrinae we see the rudiments of the stipe which reach its full development in the Oncidiinae , which is comparable to the condition seen in the Asiatic Sarcanthinae . But in the American Epidendreae , there is no stabilisation of chromosome numbers which characterises the Asiatic forms. The Epidendrinae have a stabilised number 20 or its multiples but in the advanced Maxillariinae and Oncidiinae , the number ranges from 26 to 112 . The American orchid flora as we see it today is to be considered as the result of independent lines of evolution distinct from their oriental relatives . Breiger (1960 ) has pointed out that the northern limits of Asiatic tropics were at a much more northern latitude in the early Tertiary . This faciliated free migration of the flora between North East Asia and North America . In mid-Tertiary , however, the northern limit moved down considerably thus separating the American and Asiatic tropics. It appears that the 20-chromosomed condition has been attained in the Asiatic Coelogyniae ,Cymbidiinae etc. and the American Epidendriinae independnetly.
Eventhough various species of orchids vary in their individual requirements of optimum temperature , generally orchids thrive in a day temperature varying between 60 to 70 degree F and night temperature of 55 to 60 degree F. Depending upon their preference for a particular range of temperature , the various cultivated species are categorised as cool, intermediate and warm species:
Cool species Day time temp. Night temp. 60-70 F
Intermediate species Day temp. Night temp. 65-75F, 60-65F.
Warm species Day temp.
70-85 F .
65 -70 F
Temperature influences not only proper vegetative growth, but also production of flowers in quite a good number of species . For optimum growth and flowering the night temperature should decidedly be lower than day temperature, preferably by a margin of about 10 F . This is usually so under natural conditions , but in closed orchid houses , it may be a different story altogether. So particular care should be taken in order to provide these ideal conditions. Unless light temperature is kept at a considerably lower level than during the day, the metabolic processes within the plants are not slowed down during the night , the metabolic processes within the plants are not slowed down during the night, with the result that all the reserve food materials are used up in further vegetative growth and no flowers are produced . This is the reason why many orchids of the higher altitude thrive well when brought down and cultivated in the plains , but never produce flowers. Cattleya labiata does not flower when night temperature is higher than 70 F . Most Cymbidium species need a temperature of 50-60 F.During nights and plenty of sunlight during day time , for proper flowering . It has been reported that the pigeon orchid, Dendrobium crumenatum , flowers only in response to a sudden drop in temerature of 10 F . Perhaps this is also the case with such species as Thrixspermum arachnites , Dendrobium haemoglossum, Ephemerantha fimbriata etc. which are also observed to flower greariously . Flowering in certain species of Coelogyne and nobile type Dendrobium is also supposed to be temperature controlled.
Insects which cause damage to orchids are slugs , snails , cockroaches , grasshoppers, thrips, aphids, bugs and mites. The harm they do to the plants is manifold . They feed on plant parts or suck the sap thereby exhausting the vigour of the plant . They inflict mechanical injuries to the plants , thus leaving the path clear for pathogens like bacteria which can enter the plant only through wounds. These insects, particularly the aphids, act as vectors helping to carry virus infection from one plant to another. Finally they spoil the blooms by carrying away the pollinia which makes the flower wilt within a day or two. Measures should therefore be taken to keep away all insects from orchid house.
A variety of organic insecticides of different killing potentialities are now available in the market ,which help the grower to deal with the pests effectively . Organophosphorous insecticides like Parathion , Malathion etc., chlorinated hydrocarbons like BHC ,Endrin , Aldrin ,Dieldrin etc, and pure plant products like Nicotine are widely in use now . The only disadvantage with these products is that they are as deadly to human beings as they are to insects and if used indiscriminately or without proper precautions, they can cause serious trouble to the person who is administering them .
Slugs, snails and cockroaches hide themselves in the dark corners and crevices of the orchid house . They come out only at night and feed on tender flower shoots and the growing tips of the roots , causing serious set-back in their growth.These organisms can be baited and killed with poisoned food. Metaldehyde has proved to be an effective poison in such cases . This could be kept mixed with honey or syrup . Northern (1970) has recorded that stale beer kept in thimbles at various places in the orchid house attracts the slugs. In the attempt to get a drink they get draowned in the beer . Hollowed out potatoes also serve to trap slugs and snails . Dipping the pots in a solution of the insecticide will help to flush out the cockroaches , but the snails retire to their shells and thus escape from the action of the insecticide . To avoid this, the pots are immersed in a mild solution of the insecticide overnight ,which will flush them out of their shells and kill them.
Grasshoppers fly over from outside and eat up young leaves of plants. Spraying with 10 % BHC will keep away these insects.
Thrips are very small insects, which prefer to lay their eggs on young flower buds. Upon hatching , the young unwinged thrips make their way inside the buds, which sustain injuries during the process . The flowers are disfigured and sometimes they even fail to open. Biweekly spraying with 0.1 % malathion will control this pest.
Bugs and aphids suck the sap from the plants. Some of these are brought in by ants for the honeydew which they secrete . The mealybug is easily identified by its soft , filamentous body with a coating of powdery wax . Spraying with 0. 03%endrin or 0. 02 % of parathion will destroy these nsects.
Among mites , the red spider mite causes the greatest devastation to orchids. They are red, orange or yellow in colour and difficult to see by the naked eye . They colonise on the underside of the leaves and eat up all the parenchymatous tissue. Spraying the underside of the leaves regularly with 0. 1 % malathion will help to get rid of this pest.
Scale insects attach themselves firmly to stems and leaf-veins . They not only extract juives , but also have a toxic effect upon the plant , so that if not controlled , the plant will gradually die. Because of their scales they get protection from the insecticides . Only the crawler stage, which occurs in its life history just after the eggs are hatched and which lasts for 28- 48 hours, is susceptible to insecticides . Hence for effective control, frequent application of the insecticide is necessary . Spraying fish oil soap (1 lb. in 6 gallons of water) or 0.025% of parathion is effective in eradicating this pest.
Holttum (1953) recommends the use of the root extract of Tuba (Derris ) , a plant which is very common in Malaysia , as an insecticide.
and many more see early in my next article