Codies 241 



the filaments get old they become fitted with 'stoppers' or 'plugs/ the 

 beginnings of which appear quite early in the growth of the filament. 



The parietal chloroplasts are very small and extremely numerous, 

 especially near the apices of the branches: here they may be so densely 

 aggregated that the green colour becomes of an intensity approaching 

 black. In the lateral ' palisade ' branches the chloroplasts are often grouped 

 in clusters or arranged in strings. 



The palisade branches, which are several times the diameter of the 

 medullary filaments from which they arise, are developed acropetally, and 

 they are not infrequently cut off at the constricted base by a stopper-like 

 partition. The wall at the apex is thicker than elsewhere and is in some 

 cases mucronate. It has been found that when Codium is exposed to strong 

 light it tends to cover itself with hairs. 



Reproduction occurs by the fusion of anisogametes. The gametangia 

 are produced plentifully during the winter in Codium, and are borne on 

 the upper lateral margins of the palisade branches (fig. 155 C). They are 

 elongate-ovoid bodies, usually borne singly, and finally cut off by a plug- 

 like wall from the palisade branch. Sometimes there is a succession of 

 gametangia on the same branch, scars of attachment being left as the old 

 gametangia fall away. Each gametangium has a distinctly two-layered wall, 

 the outer layer being firm and thin, whereas the inner layer is thicker and 

 able to undergo considerable swelling. The female gametangia were first 

 described by Thuret ('50) and Derbes & Solier ('56), who showed that the 

 green female gametes escaped en masse through a rupture in the apex of the 

 gametangium. This rupture has been shown to take place as a result of the 

 internal pressure exerted by the swelling of the inner layer of the gametan- 

 gium- wall. The gametes soon separate and actively swim away. The male 

 gametes, which are much smaller and of a golden-yellow colour, are produced 

 in similar gametangia, but in larger numbers. The fusion of the gametes 

 has been observed by Oltmanns ('04; consult fig. 155 DG), although 

 Berthold ('80) long ago showed that young plants could only be developed 

 after the larger and smaller motile cells had been mixed. The zygote 

 germinates at once. 



Went ('89) found both kinds of gametangia on the same individual 

 plants. His statement, that the megagametes can become parthenogenetic 

 and develop directly into new plants requires confirmation. 



Gibson & Auld ('00) have observed that the gametangia after reaching a 

 certain stage of development, may become vegetative and be transformed 

 into adventitious buds. 



Only two genera are known, both of which may possibly have been derived from 

 Cklorodesmis : Codium Stackhouse, 17951801 ; Pseudocodium Weber van Bosse, 1895. 

 In Codium the medullary filaments form an irregular plexus and the branches 



16 



w. A. 



