300 PLANT STUDIES 



sperm, the organs producing the two being known as oogo- 

 nium and antlieridinm respectiyely. 



(5) Algm the main line. — The Alga3, aquatic in habit^ 

 appear to be the Thallophytes which lead to the Bryophytes 

 and higher groups, the Fungi being regarded as their de- 

 generate descendants ; and among the Alga3 the Cliloro- 

 phyceaj seem to be most probable ancestors of higlier forms. 

 It should be remembered that among these Green Algte the 

 ciliated swimming spore (zoospore) is the characteristic 

 asexual spore, and the sexual spore (zygote or oospore) is 

 the resting stage of the plant, to carry it over from one 

 growing season to the next. 



190. General characters of Bryophytes. — The name given 

 to the group means " moss plants," and the Mosses may be 

 regarded as the most representative forms. Associated 

 with them in the grouj), however, are the Liverworts, and 

 these two groups are plainly distinguished from the Thallo- 

 phytes below, and from the Pteridophytes above. Starting 

 with the structures that the Alga3 have worked out, the 

 Bryophytes modify them still further, and make their own 

 contributions to tlio evolution of the plant kingdom, so 

 that Bryophytes become niucli more complex tluui Tliallo- 

 pliytes. 



197. Alternation of g-enerations.— Probalily the most im- 

 portant fact connected with the Bryophytes is the distinct 

 alternation of generations which they exhibit. So impor- 

 tant is this fact in connection witli the development of the 

 plant kingdom that its general nature must be clearly under- 

 stood. Prol)ably the clearest definition may be obtained by 

 tracing in bare outline the life history of an ordinary moss. 



Beginning with the asexual spore, which is not ciliated, 

 as there is no water in whicli it can swim, we may imagine 

 that it has been carried by the wind to some spot suitable 

 for its germination. It develops a bi-a,ncliing filamentous 

 growth wlii<'h resembles some of the Conferva forms among 

 the Green Algie (Kig. ,'37.5). It is prostrate, and is a rcgu- 



