ORCHIDS 



ORCHIDS 



2381 



interest on the part of cultivators, and great collec- 

 tions have grown up. To a large extent, these collec- 

 tions have been renewed from fresh importations from 

 the wild, but the recent discoveries of symbiotic rela- 

 tions in germination, as well as better understanding 

 of cultural requirements, will constantly increase the 

 domestic supply. In the culture of a wide range of 

 orchids the gardener exhibits his mastery of the arts of 

 cultivation. The recent studies in this field afford very 

 definite practical applications of scientific methods. 



Distribution. 



The orchids are distributed over all parts of the world 

 with the exception of the polar regions and the great 

 deserts. About 85 per cent of the species occur in the 

 tropical and subtropical regions. Here they are found 

 to a great extent in the mountainous districts. In some 

 parts of the Himalayan region, the orchids constitute 

 the most abundantly represented family of plants in 

 point of number of species. Most of the tropical species 

 are endemic. The widely distributed species are found 

 in the North Temperate and the Subarctic zones. They 

 include such forms as Calypso bulbosa (formerly known 

 as C. borealis), Microstylis monophyllos, Liparis Lceselii, 

 and species of Orchis (or Galeorchis). These are found 

 throughout the northern regions of both hemispheres. 

 The greater number of the orchids are distributed in 

 three regions of the earth: (1) The tropical African 

 region, including the islands to the east, furnishes com- 

 paratively few species to cultivation. These mostly 

 belong to the genera Angrsecum, Bulbophyllum, and 

 Disa. This region also contains a number of endemic 

 genera not of great interest to cultivators, and repre- 

 sentatives of such widely distributed genera as Habe- 

 naria, Liparis, Microstylis, Epipactis, and others. (2) 

 Unusually rich in genera is the region of tropical Asia, 

 including the neighboring groups of islands. Typical 

 of this region are the large genera Dendrobium, Eria, 

 and Bulbophyllum, and many smaller genera, including 

 Paphiopedilum, Co3logyne, Cymbidium, Sarcanthus, 

 Saccolabium, and Vanda. Among the genera common 

 to this region and the African region are Bulbophyllum, 

 Phaius, Calanthe, Liparis, and Microstylis. (3) The 

 tropical American region, embracing Mexico, Central 

 America, tropical South America, and the neighboring 

 islands, occupies an isolated position and consequently 

 contains an unusually large number of endemic genera, 

 many of which are represented by hundreds of species. 

 Besides the large endemic genera Epidendrum, Pleuro- 

 thallis, Oncidium, and Odontoglossum, this region con- 

 tains many of the commonly cultivated genera, among 

 which may be mentioned Cattleya, La;lia, Masdevallia, 

 Schomburgkia, Brassavola, Lycaste, Peristeria, Stan- 

 hopea, Gongora, Zygopetalum, Miltonia, Phragmiped- 

 ilum, and many others. Some 

 genera, among them Vanilla, 

 Bulbophyllum, Calanthe, 

 Liparis, and Microstylis, are 

 common to both this region 

 and the Old World. Com- 

 pared with these great flor- 

 istic regions, the temperate 

 lands of the southern hemi- 

 sphere are of less importance. 

 Of the south African genera, 

 Disa and Calanthe furnish a 

 few species valuable to culti- 

 vation. Australia contains 

 many genera in common with 

 the tropical Asiatic region, 

 but few of the cultivated 

 species are derived from 

 there. In temperate South 

 America the orchids are 



2624. Monopodial growth sparsely represented by a 

 in a vanda. fc~ vr ipeefes of Epidendrum, 



2625. 



Monopodial growth in 

 Renanthera Cathcartii. 



Oncidium, Spiranthes, Habenaria, and a few other 

 genera. From a horticultural standpoint, the species 

 of this region are of little importance. About twenty 

 genera are found in the northeastern United States and 

 Canada, mostly in swamps and moist grounds; among 

 them are the Cypripediums or lady's 

 slippers, and many beautiful plants in 

 the genera Habenaria, Pogonia, Calopo- 

 gon, Arethusa, and Calypso. 



Habited. 



With regard to their habitat, the 

 orchids are either terrestrial or epiphytic. 

 The terrestrial orchids include the species 

 of the temperate regions and many of 

 the largest and most stately orchids of 

 the tropics. Many of these are ornamen- 

 tal, even when not in flower. A few are 

 attractive on account of their variegated 

 foliage and some, like Sobralia and Sel- 

 enipedilum, are admired on account of 

 their tall graceful stems. 



Most of the terrestrial orchids 

 are green plants which obtain 

 their carbon supply from the 

 carbon dioxide of the air, but a 

 few forms either lack chlorophyi 

 entirely or possess it only in 

 traces too small for normal photo- 

 synthesis. These forms are sap- 

 rophytic in their mode of hie and 

 depend for their carbon food 

 upon the organic matter of the 

 humus. The appellation of para- 

 sites, which is sometimes given 

 to these forms, is erroneous. True 

 parasites are not known among 

 the orchids. 



In the saprophytic orchids, the subterranean part 

 is either a much-knotted coral-like rhizome devoid of 

 true roots (Corallorhiza, Epipogon), or a subterranean 

 rootstock producing numerous crowded fleshy roots 

 (Neottia, Galeola). The annual shoots are yel- 

 lowish, brownish, or reddish, without true leaves, but 

 bearing scales and a terminal inflorescence which may 

 be reduced to a solitary flower. Very curious are the 

 members of the Javan genus Galeola, whose leafless 

 climbing stems attain a height of 100 feet, ascending 

 trees by means of roots that arise opposite the scale- 

 leaves, and producing a terminal and many lateral 

 racemes in the upper part of the stem. The saprophytic 

 orchids are not cultivated except occasionally in botanic 

 gardens, as the conditions necessary for then: existence 

 are not readily imitated. 



The epiphytic orchids exhibit the most varied forms. 

 They are confined to the tropics and subtropics, where 

 they inhabit branches of trees, dead trunks, and often 

 barren rocks in exposed places. They grow mostly in 

 regions where a part of the year is unfavorable to vege- 

 tation. As an adaptation to these conditions, they have 

 developed special food reservoirs (pseudobulbs) termi- 

 nating each season's growth. In this group there are 

 comparatively few plants of attractive habit. They are 

 usually devoid of graceful foliage, each pseudobulb 

 bearing a few stiff leathery leaves. The older pseudo- 

 bulbs become shriveled and leafless, detracting from the 

 appearance of the plants, and in Pleione the plants are 

 entirely leafless at the flowering time. In some of these, 

 however, the pseudobulbs are numerous and closely 

 crowded, and retain their foliage, making plants of 

 neat compact habit (Ccelogyne, Miltonia). In their 

 mode of life, the epiphytic orchids resemble the green 

 terrestrial orchids. For their mineral nutrients they are 

 dependent upon the material which is mostly the residue 

 of decayed organic matter which accumulates among 

 their roots. They are not saprophytic or parasitic. 



