THE ORCHIDACE&. 



169 



you find it pulpy-granular. In many orchids it coheres 

 into coarse grains, held together in one mass by cobwebby 

 tissue, and known as pollinia (Fig. 457). You find just 

 such pollen masses, or pollinia, in the gynandrous stamens 

 of the milk-weed (Fig. 458). The ovary of the lady's- 



FIG. 457. 



FIG. 458. 



slipper is inferior, forming in fruit a one-celled pod, with 

 innumerable minute seeds borne on parietal placentae. 

 In some orchids you find it so twisted as to alter the posi- 

 tion of the petals. 



The characters of the Orchidaceae will be better under- 

 stood by comparing them with other groups of parallel- 

 leaved plants. Provide yourself with lilies of any sort, 

 and specimens of blue flag, or flower-de-luce. Compare 

 your lilies with the following description : 



Herbs with simple, sheathing or clasping, parallel- 

 veined leaves. Flowers regular, perfect. Perianth of six 

 parts in two circles of similar color and form. Stamens 

 six, inserted on the leaves of the perianth ; anthers in- 

 trorse. Ovary free, three-celled, with numerous ovules on 

 axile placentas ; the styles united into one. 



What number have you found prevailing in the lilies 

 you have examined ? What number occurred oftenest in 

 describing the Gompositse ? The Labiatae ? The Umbel- 



