ORCHIDS 



ORCHIDS 



2385 



ally resembles the lateral petals. Often it is movably 

 attached to the mesochil. In some forms of the 

 Pterostylidinae the labellum is sensitive, and when irri- 

 tated by an alighting insect closes sharply against the 

 column, entrapping the animal. 



2634. Odontoglossum CErstedii, a sympodial orchid with lateral 

 inflorescence, and pseudobulbs consisting of a single internode. 



The morphological center of the flower is occupied 

 by a fleshy elongation of the floral axis known as the 

 column. This is short and inconspicuous in some forms, 

 but in most species it is well developed. It is usually 

 bilaterally symmetrical. The posterior surface is con- 

 vex while the anterior surface, toward the labellum, is 

 concave. Usually the column is curved toward this 

 face. In a few forms, like Cycnoches, the curvature is 

 very marked, while in Coryanthes the column is 

 asymmetrically bent. Within the column is a canal con- 

 tinuous with the carpellary cavity. (Fig. 2642.) The 

 column is primarily of importance because at its upper 

 end it bears the stamens and 

 the stigmas and auxiliary 

 structures which function in 

 the pollination of the flowers. 

 Besides these organs, it some- 

 times bears a number of 

 outgrowths and appendages 

 which give it a very complex 

 appearance. Often the label- 

 lum does not appear to be 

 attached directly to the col- 

 umn, but is borne upon a 

 special fleshy outgrowth at 

 its base known as the "foot" 

 of the column. Between the 

 forms in which the foot of 

 the column is not developed 

 and those in which it is pres- 

 ent, no distinct line can be 

 drawn. In our native orchids 

 it is mostly absent. In Gram- 

 matophyllum there is a small 

 cuplike depression upon 

 whose anterior wall the blade 

 of the labellum is attached 

 with a narrow base. It is 

 here a matter of interpreta- 

 tion whether the anterior wall 

 of the cup is regarded as a 

 part of the labellum or as the 

 foot of the column. (Fig. 

 2643.) In other cases where 

 the foot is more distinctly 

 developed, the labellum is 

 often plainly attached to its 



2635. An orchid flower 

 (with unezpanded bud 

 above), to show the very long 

 spur. Macroplectum ses- 

 quipedale. ( X about M) 



lower side, as in Paphinia, Pescatoria, Phaius, Bulbo- 

 phyllum. (Fig. 2644.) Frequently the lateral sepals 

 are decurrent upon the foot or entirely attached to 

 it (Bulbophyllum Achrochxne, Fig. 2645). In some 

 forms the lateral sepals and the labellum are borne 

 near the end of the foot while the lateral petals are 

 decurrent upon it (Batemannia) . Sometimes the lateral 

 sepals and the labellum are carried entirely away 

 from the other parts by the elongation of the foot 

 of the column, thus giving the flowers strange and 

 fantastic forms (Drymoda, Gongora, Aerides). When 

 the lateral sepals or the petals are decurrent upon the 

 foot they, together with the labellum attached at the 

 apex, often form a "chin" or "mentum" which is present 

 in many orchids, such as Dendrobium, Pescatoria, 

 Lycaste, Batemannia. (Fig. 2646.) Frequently the 

 base of the mentum is extended below into a sac or 

 spur of various forms and length. More often the spur 

 arises from the labellum itself (Phaius, Platanthera) . 

 Within the cavity of these spurs or sacs, honey is 

 secreted, and often the walls themselves contain juices 

 which are sought by insects. 



The upper part of the column bears the stigmas and 

 the stamens. In the Diandra, the three pistils are 

 fertile, as indicated 

 by the more or less 

 evidently three-lobed 

 stigma (Figs. 2647 

 and 2648), but in the 

 Monandrse only two 

 stigmas are recep- 

 tive. The place of 

 the third is occupied 

 by the curious "ros- 

 tellum," which sepa- 

 rates the anther-bed 

 from the stigmas and 



Srevents the pollen 

 om falling directly 

 upon them (Fig. 

 2642). The stigmas 

 are usually flat sur- 

 faces sunk in a de- 

 pression in the col- 

 umn below the ros- 

 tellum. In a few 

 genera they are 

 elevated on stalks 

 (Habenaria), and in 

 Sophronitis they ex- 

 tend partly along 

 two wing-like pro- 

 jections of the col- 

 umn. The essential 

 organs, in other 

 forms, are shown in 

 Figs. 2647-2652. 



The stamens in 

 the Diandrse are 

 situated laterally on 

 the column under a shield-like staminodium which i3 

 developed in place of the odd stamen of the outer 

 whorl. In the Monandre, the stamen is situated at the 

 dorsal margin of the column. Its position is sometimes 

 erect, but more frequently it is bent downward with 

 the anther either pendent (Ccelogyne, Fig. 2650), or 

 lying in a depression, the "clinandrum" or "anther-bed," 

 in the top of the column. From the dorsal part of the 

 column a petaloid appendage often arises and extends 

 above the anther. The sides of the anther-bed are 

 formed by outgrowths of the column. They are often 

 developed as crests, ears, or winglike structures orna- 

 menting the column and enfolding the anther. The 

 floor of the anther-bed is formed by the rostellum. 



The anther sometimes remains two-celled, but more 

 frequently the cells are further divided, by longitudinal 



2636. The appendaged flower of 



Phragmopedilum caudatum. 



151 



