84 PLANT BIOLOGY 



The naturally crossed seedlings derived from the crossed plants 

 flowered in all three pots before the naturally crossed seedlings 

 derived from the self -fertilized plants. 



"The average height of the six tallest plants derived from the 

 crossed plants is 12.56 inches; and that of the six tallest plants 

 derived from the self-fertilized plants is 10.31 inches ; or as 100 to 

 82. We here see a considerable difference in height between the 

 two sets, though very far from equalling that in the previous trials 

 between the offspring from crossed and self-fertilized flowers. This 

 difference must be attributed to the latter set of plants having in- 

 herited a weak constitution from their parents, the offspring of self- 

 fertilized flowers ; notwithstanding that the parents themselves had 

 been freely intercrossed with other plants by the aid of insects." 

 (" Cross and Self Fertilization in the Vegetable Kingdom.") 



Darwin, therefore, proved conclusively by these careful 

 experiments (1) that pansy blossoms which were cross-polli- 

 nated produced ten times as many seeds as those that were 

 self -pollinated ; (2) that the plants developed from these 

 seeds, produced as a result of cross-pollination, were far more 

 vigorous and prolific ; and (3) that the descendants of the 

 plants produced by self-pollination, even when their flowers 

 were cross-pollinated, were not able to develop seeds capable 

 of as vigorous growth as the descendants of plants produced 

 continuously by cross-pollination. 



95. Prevention of self-pollination. We have found that 

 the pansy is well adapted to bring about cross-pollination, 

 and since, as Darwin proved, cross-pollination results in seeds 

 being formed which produce much more vigorous and fruit- 

 ful plants, we should expect that the pansy would have de- 

 veloped some means of preventing self-pollination ; and this, 

 as we shall see, proves to be the case. 



The anthers of the pansy, as we saw, are joined about the 

 pistil so as to form a band, and the openings for the escape of 



