Chsetophoraceas 293 



antheridial cell produces two antherozoids, which are similar in form to the 

 zoogonidia, but slightly more elongated, with shorter cilia, and of a brownish- 

 red colour (fig. 187 D}. The oogonia arise from ordinary vegetative cells by 

 an increase in size. They become ovoidal in shape and develop a thick 

 lamellose wall. Only one oosphere is formed within the oogonium, which 

 opens by a lateral pore to admit the antherozoids. After fertilization the 

 oospore develops a thick wall and a brick-red colour, but it does not fill 

 the oogonium (fig. 187 C). 



Species of Ci/lindrocctpsa are distinctly uncommon, although C. geminella Wolle is 

 perhaps the most widely distributed. They usually occur in pools and lakes among 

 aquatic macrophytes. C. involute^ the species in which Cienkowski observed the sexual 

 reproduction, is an Alga of great rarity. 



Family Chaetophoracese. 



The principal members of the Chsetophoracese have doubtless originated 

 directly from the Ulotrichacese by the branching of the thallus. In all the 

 genera except Microthamnion the branches are attenuated, but in some 

 cases the attenuation is much more pronounced than in others, as for 

 instance, in Draparnaldia, Stigeoclonium (= Myxonema), etc., in which the 

 branches are produced into long multicellular hairs. The thallus is recumbent 

 or creeping in the Ulvellese and in some of the Microthamniea3, but in the 

 Chsetophoreae only the basal portion of the thallus is recumbent and often 

 but feebly developed, the main portion consisting of erect tapering branches. 

 In the creeping part of the thallus the cells are frequently so inflated that 

 the branches are moniliform or torulose. In the erect part of the thallus 

 the cells, although often more or less tumid, are elongated, especially towards 

 the ends of the branches, the terminal cells of which are sometimes attenuated 

 to form long hyaline hairs. Setae or hairs occur, however, in a number of 

 the genera of both the Chsetophorese and Ulvellese, and they are o f various 

 kinds, usually with a lumen, but sometimes without. In the Gomontiese, in 

 which the thallus bores into the calcareous shells of Molluscs, the cells in the 

 more superficial parts are often most irregular. 



There is a single parietal chloroplast in each cell, usually plate-like and 

 more or less irregular, and containing one or more pyrenoids. In the 

 attenuated cells towards the ends of the branches of many of the Chaatophorese 

 the chloroplast becomes reduced, and the long hyaline terminal cells and 

 setas have no chlorophyll. 



Asexual reproduction generally occurs by zoogonidia which exhibit a 

 considerable range in size, the smaller ones being termed microzoogonidia 

 and the larger macrozoogonidia. They possess either two or four cilia and a 

 pigment-spot, and they may be produced in any cell of the thallus except 

 those forming the rhizoids or the terminations of the branches. In most of 



