CHLOROPHYCE^ 133 



of reproduction, viz. by zoospores. It is consequently 

 an aberrant type, but its inclusion may be justified 

 on grounds dealt with later. 



The Thcdlus. The beautiful feather-like fronds of 

 Bryopsis recall the habit of certain species of Caulerpa, 

 but between the genera there is little more than this 

 superficial resemblance. Wille has stated that in 

 old stalks of Bryopsis trabeculae sometimes occur, but 

 the observation is open to question. If established, 

 it would certainly help in the elucidation of the 

 position of Caulerpa, especially when taken together 

 with the observation of Correns (p. 124) on the 

 character of the cell-membrane. The thallus of 

 Bryopsis consists of a single branching cell differ- 

 entiated into rhizoids and erect shoots. The shoots 

 consist each of a primary stalk, which either itself 

 bears the ultimate lateral branches (which for con- 

 venience may be called leaves with apologies to 

 formal morphology) or it may first branch repeatedly. 

 The variations in this respect and in the occurrence 

 of the leaves, whether opposite, alternate, secund, or 

 in irregular spirals round the stalk, are characters of 

 use in the discrimination of the species, though they 

 are to be used with caution, since variation occurs 

 within certain limits. The erect feathery fronds of a 

 beautiful deep green are not only very graceful, but 

 furnish objects of much interest for the microscopical 

 study of the cell. In the middle of the cell is a 

 vacuole, and the protoplasm lining the wall contains 

 numerous nuclei and oval, flat chromatophores, each 

 with one pyrenoid. Bryopsis, like Derbesia, Vaucheria, 

 and Caulerpa, has all its filaments free, and not 



