HaXosphserese 



215 



[It is necessary to mention here the genus Characiopsis founded by Borzi in 1895 to 

 include a number of Algse previously described as species of Characium. It is distinguished 

 by the possession of two or more parietal chromatophores, the absence of pyrenoids, and 

 the storage of oil as a reserve ; it thus belongs to the Heterokontse.] 



Fig. 141. A and B, Characium graciliceps Lambert, x 540 ; A, typical specimen; B, showing 

 one of the early stages in the division of the protoplast; py, pyrenoids; r, 'rhizoids.' 

 C E, Characium Sieboldi A. Br. ; C, vegetative cell ; py, pyrenoid ; D, large cell from 

 which zoogonidia are escaping laterally ; E, zoogonidium ; all x about 540. FH, Sykidion 

 Droebakense Wille ; F, formation of zoogonidia ; G, showing formation of aplanospore ; 

 H, zoogonidium ; all x 513. (A and B, after Lambert ; CE, after A. Braun ; FH, after 

 Wille.) 



Sub-family HALOSPH^ERE^E. This sub-family includes only the one genus 

 Halosphwra Schmitz (1878), an Alga which is confined to the marine 

 plankton. The cells are large and spherical (fig. 142 1 and 2), attaining a 

 diameter of 600 fi, and float freely in the sea. The cell-wall is thin and the 

 cytoplasm is mostly in a parietal layer. There is one nucleus, usually in the 

 parietal cytoplasm but occasionally occupying a central position, in which 

 case the small amount of cytoplasm surrounding it is connected by radiating 

 strands with the parietal layer. In the young cell there are numerous 

 parietal discoidal chloroplasts, but in older cells these apparently fuse to form 

 a reticulum 1 . As the cells grow in size there is a repeated ecdysis of the 

 cell-wall. 



Reproduction takes place by biciliated zoogonidia of conical shape, the 

 cilia being attached to the broad base of the cone, which is therefore anterior. 

 This anterior end is also lobed at the periphery (fig. 142, 4)- The formation 

 of zoogonidia commences by the repeated division of the nucleus, the numerous 



1 A similar condition exists in many genera of the Siphonocladiales, where the reticulated 

 chloroplast is really formed by a fusion of a number of small parietal plates, which may in some 

 cases be quite separate. 



