504 



PART IV. CLASSIFICATION'. 



represented by an anterior staminode. The anther usually has 

 four pollen-sacs, but may have two (e.g. Collabium) or eight (e.g. 

 Calanthe, Bletia). In some genera the pollen- grains are separate 

 from ea.ch other ; in the majority they are united into a mass, 

 pollinium, which fills an entire pollen-sac (Fig. 244 E, F, p). The 

 pollinium may consist of tetrads with a common exine (e.g. Neottia) ; 

 or of larger groups of cells, termed massulce (e.g. Orchis), when it 

 is said to be sectile ; or of uniform tissue. In those Orchids which 

 have pollinia, it is frequently the case that the tissue of the pollen- 

 sac is prolonged, according to the position of the anther, either to 

 the lower (basitonous, e.g. Ophrydinse) or to the upper end of the 

 anther (acrotonous, e.g. Phajiinse, Oncidiinae), and here almost 

 exclusively gives rise to a mucilaginous filament, the caudiclc, 



FIG. 315. Diagram of Orchidaceous 

 flowers, neglecting resnpination. A The 

 monandrous type. S The diandrous type 

 (Cypripedium) : the shaded stamens are 

 staminodia. 



FIG. 316. F owerof Orchis mascula (x2) 

 / the twisted ovary a a a the three outer 

 perianth-leaves ; i i two of the inner, I the 

 third inner perianth-leaf, the labellum, with 

 (sp) the spur; 71 stigma; p pollen -sacs. 



attached to the pollinium (or to the two or more pollinia of each 

 half of the anther) below or above. 



The ovary is unilocular (rarely trilocular as in some Cypri- 

 pediinse), and contains numerous anatropous ovules on three 

 parietal placentae. In all the monandrous Orchids, the anterior 

 lobe of the trilobate stigma is not susceptible of pollination, and 

 is either rudimentary or develops into an organ termed the 

 rostellum (Fig. 244 ft), which is situated either above or below 

 the anther, and in the tissue of which one or two small masses 

 of sticky mucilage (retinacula) are formed, and are frequently 

 enclosed in one or two pouches (bursiculcv) formed by the rest of 

 the tissue of the rostellum. The pollinia adhere to the retinacula 

 by the caudicle, when present, and are removed, in pollination, by 

 the adhesion of the retinacula to the proboscis of the insect (see 

 p. 413). 



