240 THE FLOWER. 



Scrophulariacese, Orchidacese, &c. Nature is not prodigal, and 

 does not endow with needless adaptations flowers which are 

 otherwise provided for. 



3. ADAPTATIONS FOR CLOSE FERTILIZATION. 



432. Even where cross-fertilization in bisexual flowers is 

 obviously arranged for, it is apt to "be tempered with more or 

 less of close- fertilization. The more exquisite the arrangements 

 for the former are, the more completely is the plant dependent 

 upon insect visitation. Failure to intercross is a remote and 

 small evil compared with failure to set seed at all. In order 

 therefore that the plan of cross-fertilization may not defeat even 

 its own end, through too absolute dependence on precarious 

 assistance, some opportunity for self-fertilization will usually be 

 advantageous. Also there is a long array of insect-visited 

 flowers, especially polyandrous ones, in which close fertilization 

 must be much the commoner result, except where the pollen of 

 another but wholly similar flower has greater potency. 



433. Subsidiary self-fertilization is secured in a great variety 

 of ways. In Gentiana Andrewsii, which is proterandrous, and 

 usually cross-fertilized by humble-bees entering bodily into the 

 corolla, an exposed surface of pollen long remains fresh upon 

 the ring of anthers girding the base of the style : when the stigmas 

 separate, they remain for some days simply divergent, but they 

 at length become so revolute that the receptive surface is brought 

 into contact with the ring of pollen below. The opening and 

 closing of blossoms by day or night, the growth of style, fila- 

 ments, or corolla after anthesis commences, or other changes of 

 position, may secure a certain amount of self-fertilization in a 

 subsidiary or even in a regular way. Then certain species, such 

 as Chickweed, which blossom through a long season, close- 

 fertilize even in the bud in early spring, when insects are scarce, 

 but are habitually intercrossed by insects in summer. Somewhat 

 similarly, according to Hermann Mueller, 1 certain species, such 

 as Euphrasia officinalis and Rhinanthus Crista-galli, habitually 

 produce two kinds of blossoms, one larger and more show}-, 

 usually affecting sunny localities, and with parts adapted to 

 intercrossing bj- insects ; the other smaller or inconspicuous, and 

 with anthers adjusted for giving pollen to the adjacent stigma 

 without aid. There are gradations between these last arrange- 

 ments, and the more special and remarkable one of dimorphism 

 with 



1 Befruchtung der Blumen durcli Insekten, 294 ; Nature, viii. 433. 



