92 THE STORY OF THE PLANTS. 



the stamens ripen first, and after them the 

 carpels. How does this ensure cross-fertilisa- 

 tion ? Why, if the bee comes to a flower in the 

 first or male stage, in which the stamens are at 

 their full, and discharging pollen, the sensitive 

 surfaces or stigmas of the carpels will yet be 

 immature, so that he cannot fertilise them with 

 pollen from their own blossom. He can only 

 collect there, without disbursing anything. But 

 as soon as he comes to a flower in its second or 

 female stage, with the carpels ripe, and their 

 sensitive surfaces sticky, he will rub off some 

 of the pollen he has thus collected, and so cross- 

 fertilise the flower he is visiting. 



Each buttercup thus goes through two stages. 

 First, its stamens ripen from without inward, till 

 all have shed their pollen and withered. Then 

 the carpels ripen in the same order, till all have 

 been fertilised by the appropriate insect. Each 

 carpel here contains a single seed, which begins 

 to swell as soon as the ovary is impregnated. 



We may take it that some such flower as that 

 of the bulbous buttercup represents the original 

 ancestor of all the buttercup group, from which 

 other kinds have varied in many directions. 

 Omitting for the present all questions as to the 

 fruit and seed, which we must examine at length 

 in a later chapter, I will now proceed briefly to 

 describe a few of these variations in the butter- 

 cup family. 



The true buttercups themselves are distin- 

 guished from all other members of the group by 

 having a tiny scale over the nectary or honey- 

 gland at the base of the petal, or at least by 

 having the nectary itself as a visible pit or small 

 depression. Almost all of them are yellow, though 



