CHAP. IV.] REPRODUCTION OF PLANTS. 121 



antheroids swimming freely in the water until they 

 came in contact with the oospheres. The various at- 

 tempts of ancient aquatic types to establish themselves 

 on dry land was finally accomplished through the liver- 

 wort (HepaticoB) and moss [Musci) groups, which form a 

 connecting link between the primordial aquatic Algae 

 and the dry land vegetation of the present day ; never- 

 theless the mode of fertilization by means of motile 

 antherozoids that reached the oospheres by swimming 

 in water was so strongly stereotyped that, as already 

 stated, it held good through the liverworts {Hepaticos), 

 mosses {Musci), horsetails (Uquisetacece), ferns {Mlices) , 

 club-mosses (Lycopodiaeece), and other groups consti- 

 tuting the Cryptogams, even after these groups had 

 become much modified in other respects to enable them 

 to live surrounded by dry air, and the tardiness dis- 

 played in effecting a corresponding change in the mode 

 of efiecfcing fertilization is the main reason why the 

 above groups are more limited in their distribution, and 

 take a back place in the social scale of vegetation 

 growing on dry land at the present day. The drawback 

 alluded to is due to the fact that the sexual mode of 

 reproduction necessitates the presence of water to enable 

 the motile antherozoids to come in contact with the 

 oospheres ; hence Cryptogams are as a group confined 

 to damp situations, or the sexually produced repro- 

 ductive bodies are formed during the winter, as seen 

 in our mosses, that look bright and vigorous during 

 that period of the year, and shrivel- up during the 

 summer if growing in dry situations, conditions that 

 are not followed by those members of the plant world 

 that have made most progress. 



