STONEWORTS 



193 



below; but here the branches are in one terminal whorl 

 and are united into an umbrella-like structure. They 

 generate by biciliated isogametes. They occur in shal- 

 low tropical or sub-tropical marine w^aters. 



292. In the Stoneworts (Charales) we find the highest 

 development of the coenocytic structure. The plants 

 are erect, slender, cylindrical rows of coenocytes, rooted 

 below, and bearing many whorls of free branches. The 

 stems are often corticated with a parallel layer of smaller 

 coenocytes. They occur in the fresh or brackish waters 

 of ponds and lakes. 



293. The generation of Stoneworts is heterogamous, 

 that is by the union of bicihated sperms, with non-ciliated 



eggs. The sperms are pro- 

 duced in compound antherids 

 which are globular many- 

 celled bodies, in the interior 

 of which certain multicellular 

 filaments (the antherids) pro- 

 duce the sperms singly in the 

 cells. Each sperm is a spiral 

 thread of protoplasm, provided with two long cilia at 

 one end, by means of which it swims rapidly through 

 the water. 



294. The oogone is a single cell, which soon becomes 

 covered (corticated) by the growth from below of a layer 

 of five spirally wound coenocytes, which are prolonged 

 into a 5- or 10-cclled crown. This covering, which here 

 develops before fertilization, is analogous to the protec- 

 tive covering which in Coleochaete, forms after fertiliza- 

 tion has taken place. In the oogone is the egg, which is 

 non-ciliated, and very much larger than the sperms. 



295. The sperms enter the opening at the apex of the 

 oogone and one of them entering the egg fertilizes it. 



13 



Fig. 84.— Chara. 



