134 



open flowers, Some of our violets and polygalas produce 

 two kinds of flowers. The early ones are irregular and 

 adapted to insect pollination. In the late flowers, which are 

 closed, the pollen has been reduced to a minimum. 



In a large number .of plants self-fertilization is the rule. 

 But many of these are occasionally self-fertilized so that the 

 rule is not invalidated. But there are plants which have 

 have special arrangements for securing self fertilization, 

 as in some buttercups {Ranunculus) sandwort (Spergula), 

 willow herb (Iipilobium), but these may also be cross 

 fertilized occasionally. But there are cases in which there 

 are no chances for cross-fertilization. Such are plants which 

 produce cleistogamous or closed flowers. These, according 

 to Darwin'", occur in twenty-four natural orders. But 

 additions are constantly made, and Hemsley believes that 

 they occur in nearly all the natural orders. In many plants 

 which produce these closed flowers, irregular insect pollin-; 

 ated flowers are produced. These closed flowers produce a 

 minimum of pollen, but an abundance of seed; much more 

 so than do the flowers of the same plant pollinated by insects 

 and therefore possibly cross-fertilized, ftome of our violets 

 Viola palmata var. cucullata) often have these cleisto- 

 gamous fli)wers, and although my observations are not 

 crucial, I have seen the seeds in their pods much more 

 abundant than in the irregular flowers produced early in the 

 season. This is certainly the case in the dog violet ( Viola 

 canind). All of the plants that produce cleistogamous 

 flowers also have those of other kinds; not always in the 

 same locality, as in a small rush {Juncus bufonius)- In 

 some places this plant produces closed only, while in other 

 parts perfect flowers are produced. 



17 Different forms of flowers. 



