POLLINATION 107 



pollinated, and there is no possibility of self-polli- 

 nation. 



Second, dichogamous flowers. In hermaphro- 

 dite or bisexual flowers, from the proximity of the 

 stamens to the pistil, it is natural to suppose that 

 these flowers are self-pollinated. But on a closer 

 examination it is found that in several hermaphrodite 

 flowers the two sexes mature at different times, so 

 that the chances of self-pollination are wholly elimi- 

 nated. Flowers of this nature are described as dicho- 

 gamous. They are either protandrous or proto- 

 GYNOUS, according as the androecium or gynoecium 

 ripens first. 



Third, homogamous and herkogamous flowers. 

 Many hermaphrodite flowers mature their sexes at 

 the same time, and are therefore known as homo- 

 gamous as opposed to dichogamous. Even in 

 homogamous flowers, where self-pollination seems 

 most natural, several contrivances and adaptations 

 are met with which wholly prevent self-pollination, 

 and help to bring about cross-pollination. Such 

 homogamous flowers have been termed herko- 

 gamous. 



Fourth, dimorphic flowers. Amongst homo- 

 gamous flowers there are several in which the floral 

 adaptations are such that they favour cross-pollina- 

 tion without wholly excluding the chances of self- 

 pollination. As a matter of fact, these flowers are 

 usually cross-pollinated; but if cross-pollination fails 

 they have recourse to self-pollination. A striking 

 floral adaptation of this kind is heterostyly, a 

 condition met with in some species of plants. These 

 plants produce dimorphic flowers, or flowers of two 

 different forms (fig. loi). In one form the style is 

 long and the stamens short, and in another form the 



