35 8 PLANT LIFE. 



and lodged there. It has been clearly shown not only that 

 adaptations for securing this result have been developed, but 

 also that there have arisen various ingenious adaptations to 

 secure cross-pollination and to prevent close-pollination. 

 (See ^f 358.) Some of these may be here enumerated. 



482. Adaptations for cross-pollination. — (a) The sepa- 

 ration of the stamens and pistils, staminate flowers and pistil- 

 late flowers being produced upon the same plant or even upon 

 different plants of the same species ; (b) the early ripening of 

 the stamens so that they discharge their spores before the 

 stigma of the same flower is exposed or receptive, or vice 

 versa; (c) arrangements preventing the pollen from reaching 

 the stigma of the same flower, which vary according to the 

 different modes by which the transfer of the pollen is made; 

 (d) the failure of fertilization to occur when close-pollination 

 happens. In such cases the pollen is said to be impotent. 

 This means that the male plants are either not completely 

 formed by it, or that their sperms do not stimulate the egg 

 to development. 



483. Adaptations for close-pollination. — But close-pollin- 

 ation, even though it results in weaker offspring, is better 

 than entire failure to produce progeny. Therefore, some 

 plants permit close-pollination in the event of failure to 

 secure cross-pollination, while a few have adaptations which 

 insure it. Our common violets produce in the late spring 

 and early summer inconspicuous blossoms which do not open, 

 containing stamens with few pollen grains. These flowers, 

 however, produce seed abundantly, and always by close- 

 pollination. Various other species have similar arrange- 

 ments. 



484. Adaptations to insects.— The adaptations to secure 

 cross pollination through the visits of insects are so numerou 

 and so varied, and the advantage in the number and weight 

 of seeds produced is so marked, that for most seed plants 



