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 waters. 
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 biciliated sperms, with non-ciliated 
eggs. The sperms are pro- 
duced in compound antherids 
Sy which are globular many- 
celled bodies, in the interior 
d of which certain multicellular 
filaments (the antherids) pro- 
Wea bi ices 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-celled 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. 
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