202 



PRACTICAL BOTANY 



186. Increase in complexity of sex organs and gametes. It 



is to be especially noted that in other algae which we have 



studied reproduc- 

 tive bodies were 

 formed from cells 

 which at the out- 

 set were vegeta- 

 tive cells. In Vau- 

 cheria sex organs 

 are made primarily 

 for the work of 

 reproduction, an 

 interestmg divi- 

 sion of labor in 

 the plant. In some 

 green algae, as 

 GEdogonium (Figs. 

 1H4 and 165), 

 vegetative cells 

 are thus formed 

 into oogonia and 

 antheridia. 



It is also im- 

 portant to note 

 that in Ph'uro- 

 coccus the entire 

 plant might divide 

 ^'egetatively into 

 two new plants ; 

 or, in relatives 

 of Ph'urococcus, 

 the entu-e plant 

 might become a 

 spore ease (spo- 

 rangium), producing zo()spores. In OJadophora, zoospores are 

 formed, together witli zoospore-like gametes, the latter uniting 



Fig. 165. Reproduction in CEdogonium nodosum 



A, holdfast cell and two vegetative Cells; B, part of 

 a plant in whicli are an oogonium (o), containing egg, 

 and two groups of antheridia (a) , which have not yet 

 formed sperms ; C, part of a plant in whicli is an oogo- 

 nium (o), which, by breaking away of one vegetative 

 cell, has made a place for the sperm to enter, so that a 

 fertilized egg or oospore has been formed, as is shown 

 by its heavy inner wall ; D, a zoospore of Qidogoniuiii, 

 — D redrawn from Pringsheim. All greatly enlarged 



