VEGETATIVE AND SEXUAL REPRODUCTION 173 



A very large number of species in the different families of 

 flowering plants have their flowers adapted to cross-pollination 

 and close-pollination. In some cases these adaptations are effected, 

 as in the pea family, by irregularities in the shape of the corolla 

 and by the relative position of the anthers below the stigma. In 

 other instances the anthers ripen before the maturing of the stigma 

 in the same flower, or vice versa, thus insuring against self-pollina- 

 tion. Again, there are some plants in which the pollen of a 

 given flower will not germinate and form a pollen tube on the 

 stigma of the same flower, but will do so on stigmas of other 

 flowers of the same species. His observation of these various ar- 

 rangements led Darwin to suspect that cross-pollination was in 

 some way beneficial to plants, and resulted in his well-known 

 experiments which established the general theory of the bene- 

 ficial results of cross-pollination in the vegetable kingdom. These 

 experiments and results will be considered in some detail in the 

 next chapter, after a brief discussion of the terms commonly 

 used in plant breeding. 



