145 PHYSIOLOGICAL BOTANY. 



either be, 1st, parts of the same flower ; or, 2d, of other flowers 

 of the same plant ; or, 3d, of the same species ; or, 4th, of 

 closely related species. In the first and second cases the process 

 may be called self-fertilization ; in the third case, cross-fertili- 

 zation ; in the fourth case, hybridization. 



45 9 b. Now whether the first, second, or third process shall pre- 

 vail in any given species will depend on the structure, number, 

 arrangement, of the floral organs. In the few flowers which 

 never open, the Cleistogenes, such as the late apetalous flowers 

 of the Blue Violet, and also probably those of Gentiana An- 

 drewsii, only self-fertilization is possible. But in the multitude 

 of open flowers with both stamens and pistils exposed, as in the 

 Lily, Eose, Morning Glory, either self- or cross-fertilization is 

 possible unless determined by some other special circumstance. 

 The stigma may receive pollen directly from its own stamens, or 

 indirectly from other flowers near or remote, through the agency 

 of winged insects, humming-birds, or of the wind. Again there 

 are flowers in which the organs are so situated that self-fertili- 

 zation is very difficult, or even impossible. Of this class are the 

 Asclepiads and Orchids, whose pollen, cohering in masses (pol- 

 linia) is inclosed in cavities, and only dragged forth by insects 

 to be carried to other flowers. So in Iris, where the extrorse 

 anthers and petaloid stigmas are averted from each other, the 

 former beneath, and shedding its pollen downward. 



45 9c. Dichogamous Plants. In some species the stamens 

 and pistils are not cotemporary in the same plant, but the sta- 

 mens of one plant mature at the same time with tne pistils of 

 another plant, and vice versa. This necessitates cross-fertiliza- 

 tion, and the agency of the wind or of insects. We have exam- 

 ples in the Grasses, the common Plantain, in Scrophularia, etc. 



45 9d. Dimorphous Plants are such as the Mints (Men- 

 tha), the Yellow Jessamine (Gelsemium), Houstonia coerulea, 

 etc. In these the flowers assume two forms, with the stamens 

 and pistils cotemporary in both. In some the stamens are ex- 

 serted and pistil included, while in others the stamens are in- 

 cluded and style exserted. This arrangement also favors cross- 

 fertilization through insect agency. 



