192 



THE ALG.E 



The fertilized egg becomes an oospore within the oogonium 

 and is further protected by a cellular envelope (Fig. 185, B) 

 developed from short filaments which grow up around the 

 structure (Fig. 185, A, /), making a conspicuous fructification. 



The oospore germinates the 

 following spring, forming 

 within itself a small group 

 of cells (Fig. 185, C), each of 

 which gives rise to a zoo- 

 spore. The decay and ruptur- 

 ing of the fructification allows 

 the zoospores to escape and 

 start new Coleochcete plants 

 at the beginning of each sea- 

 son. The fructification of Co- 

 leochcete serves to multiply 

 FIG. 185. Coleochcete pulvinata 



the number 01 zoospores pro- 



A, filaments with an oogonium o, antherid- 

 ium a, and a sperm above; /, fertilized duced by the OOSpore, which 



egg in its oogonium becoming surrounded ig c l ear l y an advantage, 

 by short filaments from the cell below ; ^ 



Coleochcete stands at 



It, oospore completely inclosed in a cel- 

 lular envelope derived from filaments such 

 as are shown in A,f; C', germination of 

 oospore, each cell in the interior develops 

 a zoospore. After Pringsheim 



the 



head of one of the best-de- 

 fined lines of evolution in the 

 algae, a line which starts at 

 the lowly level of the Ulotliricacece and runs upwards through 

 the Chcetophoraccce. Authors have generally regarded these 

 forms as leading almost directly to the bryophytes, with Coleo- 

 chcete just a little below the liverworts ; but, as we shall see 

 later, there are serious difficulties in the wav of this view. 1 



/ 



Nevertheless, these forms are perhaps nearer than any other 

 living algre to the theoretical main line of ascent. 



1 The fructification of Coleochcete has been regarded as similar to the so- 

 called fruit or sporophyte of the liverworts, but, as explained in Sec. 336, 

 there is strong evidence against this interpretation. The one-celled sexual 

 organs of ColeocfiTte are also very different from the many-celled sexual 

 organs of the bryophytes, and this is also evidence against the existence of a 

 close relationship between the groups (see Sec. 299). 



