102 Principles of Plant Culture. 



151. Cross-Pollination occurs when the stigma re- 

 ceives pollen from a different plant, especially from a 

 plant of a different variety or species (21). The fec- 

 undation resulting constitutes a cross or hybrid, as the 

 case may be (23). Cross-pollination is often performed 

 artificially (440). 



Close- or self-pollination occurs when the stigma re- 

 ceives pollen from its own flower or plant. 



152. Cross-Pollination is Advantageous in plants, as 

 Darwin 's ' careful experiments have shown. The seeds 

 formed are usually more numerous and larger and 

 make more vigorous plants than with close-pollination. 

 Especially is this true when the parent plants have 

 been subjected to different growth conditions in pre- 

 vious generations. Nature favors cross-pollination in 

 perfect-flowered plants by numerous adaptations tend- 

 ing to prevent self-pollination, as maturing the pollen 

 either before or after the receptive stage of the stigma, 

 or so locating the stamens that the pollen is not readily 

 deposited on the stigma of the same flower.* In some 

 eases, pollen is infertile on the stigma of the same flower 

 or plant that is abundantly fertile on stigmas of other 

 plants of the same species (154). 



153. Perfect,* Monoecious (mo-nce'-cious) and Dioe- 

 cious (di-ce'-eious) Flowers. Flowers containing both 

 stamens and pistils (or pistil), as in the apple, tomato, 

 cabbage, etc., are called perfect or hermaphrodite (her- 

 maph'-ro-dite) ; those containing but one of these or- 

 gans, as in the melon, Indian corn, etc., are called im- 



* Darwin's work "On the Various Contrivances by which Orchids 

 are Fertilized by Insects" describes many most interesting adaptations 

 of this sort. 



