REPRODUCTION. 239 



toward the arcliegonia. It is a cTiemical agent. Among ferns it 

 is malic acid, among leafy mosses it is cane-sugar, which acts as the 

 peculiar stimulus that attracts the spermatozoids to the opening 

 of the archegonium. Among phanerogams the pollen-grains are 

 transferred to the stigma (or micropyle) by means of insects or the 

 Avind. Plants dependent upon the wind for pollination are said to 

 be anemopMlous ; those dependent upon insects are entomophi- 

 lous. In some plants pollination is dependent upon water-cur- 

 rents ; they are said to be hydrophilous. 



The great majority of phanerogamic flowers are structurally 

 adapted to be fertilized by other flowers of the same species ; they 

 are open at the appropriate time : chasmogamous flowers. There 

 is also a small group of plants dependent upon self-fertilization and 

 whose flowers therefore remain closed : cleistogamous flowers. Ex- 

 ample : Ranunculus aquatiUs. 



A study of these relations gives us an insight into a large num- 

 ber of adaptive arrangements. Some of the subsequent statements 

 are repetitions, but will not be amiss, because of the importance of 

 the subject. The anemophilous plants have inconspicuous flowers 

 of dull colors and very numerous pollen-grains ; they sometimes 

 bloom before the appearance of the leaves. Examples : Gymno- 

 spermce and Graminece. In the former [Pinus) the pollen-grain 

 may have winged appendages. The entomophilous flowers require 

 and possess large showy flowers, with odor and nectaries for the 

 purpose of attracting insects. 



From the frequent occurrence of hermaphroditic flowers among 

 phanerogams it must not be concluded that self-pollination is the 

 rule. The majority of hermaphroditic flowers as well as flowers 

 in general are specially adapted for the process of cross-pollination. 

 Of such adaptations the tliree following may be mentioned without 

 considering the mechanical structures thereby involved. 1 and 3 

 refer to hermaphroditic flowers. 



1. Dichogamy. The andrcecium and gynoecium of the same 

 flower do not mature at the same time. If the anthers mature first, 

 it is known a,^ protandry {Compositcp) ', if the pistil matures first, 

 it is known as protogyny (as in Plantago 7nedia). Though cross- 

 pollination is the rule, hermaphroditism is not an unsuitable ar- 

 rangement; by it is represented the largest possible number of 

 flowers of both sexes with the least expenditure of substance. 



