SEED-BEARING PLANTS 
501 
Of about 24,000 known species of monocotyledons, 
over one-fourth are orchids. The number of individuals, 
however, of any given species is small, as compared, for 
FIG. 387. Floral organs of an orchid (CaUleya sp.). A, the entire 
flower; sep, sepal; pet, petal; B, column, showing s, stigma and r, the ros- 
tellum (beak), with the small glands at the tip; to the glands are attached 
the four strap-shaped caudicles of the pollinia; C, pollinia, with the four 
caudicles; below, the gland; D, longitudinal section of the column; p, 
pollinium; E, the same, enlarged. (Cf. Fig. 386.) 
example, with the grasses. The most highly modified 
forms are tropical, and are seen in temperate regions 
only in plant-houses. 
