ORCHIDS 



ORCHIDS 



2383 



being enlarged into a distinct pseudobulb (Epidendrum 

 spp.)- 



An equally varied display is presented by the sym- 

 podial orchids having a lateral inflorescence. Nearly 

 stemless forms, or forms in which the stem is developed 

 as a subterranean structure often of curious configura- 

 tion, occur in the 

 Phaiinse (Phaius, 

 Calanthe, Bletia), 

 the Cyrtopodiina3 

 (Lissochilus, War- 

 rea), and the Cor- 

 allorhizinse (Cor- 

 allorhiza, Apleo 

 trum). In others, 



the stem is devel- 

 b 



2628. Dendrobium, diagrammatic sketch 

 showing growth of sympodial orchid. The 

 dark and light parts, a a and b b, repre- 

 sent each the growth of one shoot. 



oped as a pseudo- 

 bulb consisting of 

 several internodes 

 clothed with 

 leaves ( Cymbid- 

 ium, Mormodes, 

 Catasetum, Chy- 

 sis), or it is elong- 

 ated and caneJike 

 as in Dendrobium, 

 which, however, 

 may belong to 

 the terminal-flow- 

 ered forms since 

 some of the near relatives of this genus produce ter- 

 minal flowers. In species of Grammatophyllum and 

 Cyrtopodium, the tall leafy pseudobulbous stems attain 

 magnificent proportions, reaching a height of 3 to 15 

 feet. (Fig. 2633.) In the greater number of the lateral- 

 flowered forms, only a single internode of the stem is 

 enlarged to form a pseudobulb. (Fig. 2634.) Such is 

 the case in Odontoglossum, Oncidium, Bulbophyllum, 

 Trichopilia, Zygopetalum, Lycaste, Stanhopea. 



The inflorescence of the orchids is throughout of the 

 indeterminate type, that is, truly terminal flowers are 

 not produced. Even in those cases in which the flower is 

 solitary, the presence of a few bracts above it show its 

 axillary position. In the monopodial orchids, the 

 inflorescence is of necessity always axillary since the 

 growth, of the vegetative shoot is indeterminate, but in 

 the sympodial orchids it may be either axillary or 

 terminal, as described above. In Coelogyne cristata, and 

 a few others, the inflorescence is terminal on special 

 branches of the sympodium. 



The form of the inflorescence is various. Solitary 

 flowers occur in many genera, as Cypripedium, Lycaste, 

 Anguloa, and others, but more commonly the inflores- 

 cence is racemose or paniculate. The raceme may be 

 close and compact as in some of the monopodial orchids 

 (Aerides, Saccolabium), or loose with few to many 

 flowers, as in most of our native orchids as well as in 

 most of the commonly cultivated species. In Renanthera, 



the gigantic racemes 

 attain a length of many 

 feet. Large paniculate 

 inflorescences are 

 characteristic of some 

 species of Oncidium 

 and related genera. 

 The inflorescences are 

 sometimes of a climb- 

 ing habit and attain a 

 height of several yards. 

 The large perennial 

 panicles of some species 

 of Phalsenopsis bear as 



*> f ** many as 200 flowers. 



2629. Cattleya, showing a sympo- T Vr ,, 



dial growth. The light and shaded In Vanilla, large ra- 



parts, a a and 6 b, each represent cemes arise from the 



one year's growth. axils of the Upper 



leaves so that the whole upper part of the plant may 

 be considered as a huge panicle. 



Morphology of the floral parts. 



No group of plants exhibits so great variety of modi- 

 fications of the floral structures as the orchid family. 

 Some of the forms are shown in Figs. 2635, 2636, 2637. 

 Fundamentally the flower is of the liliaceous type; but, 

 by the supression of some parts and the modification 

 of others, the structure of the flower has been so changed 

 that in its outward appearance it bears little resem- 

 blance to the typical monocotyledonous flower. In 

 flowers of the liliaceous type, there are normally present 

 two outer whorls of floral organs, the sepals and the 

 petals, two whorls of stamens, and an inner whorl 

 representing three carpels. In the orchid flower, the 

 two outer whorls, the sepals, and petals are developed. 

 Of the stamens, only two are fertile in the Diandrse 

 (Cypripedium and related genera), while in all the 

 other orchids (Monandrse) only a single stamen is 

 fertile. The three carpels are always present. The three 

 corresponding stigmas are developed in the Diandrse, 



2630. The tuber formation of terrestrial sympodial orchids, 

 a, b, c, d, young seedling stages of Orchis militaris; e, section 

 through the same; / and g, plants the following spring with the 

 tubers completed; h, section showing beginning of lateral shoot; 

 i, tubers of mature plant; j, longitudinal section of same; k, 

 tubers of Orchis latifolia. 



while in most of the remaining orchids only two stigmas 

 are receptive (Monandrae). (See Fig. 2638.) 



The relation of the parts of the flower to one another 

 is greatly changed by the growth of the floral axis. 

 This is convex in the very young stages of development 

 but it soon becomes cuplike by the cessation of growth 

 of the center and the more rapid growth of the periph- 

 eral zone. A hollow or tubular axis is thus produced, 

 within which are formed three longitudinal ridges or 



Slacentae upon which the ovules are borne. The hollow 

 oral axis constitutes the "inferior ovary" of the 

 orchids (Fig. 2639) and at the same time acts as the 

 stalk or pedicel of the individual flowers of the 

 inflorescence. The ovary is structurally 3-celled. (Fig. 

 2640.) Besides the carpellary cavity, the axis of many 

 orchids contains another cavity which lies toward the 

 labellum or lip and opens at the base of it. This is a 

 nectary. It may be considered in the nature of the 

 cavity of an adnate spur of the labellum. In the 

 embryonic state, the orchid flower is so oriented that 



