Rhizoclonieae 



267 



Sub-family RHIZOCLONIE^:. The filamentous thallus of these Algse is 

 branched, or less frequently unbranched. There is, as a rule, a basal rhizoidal 

 attachment (fig. 171 F and G). In Spongomorpha the branching is consider- 

 able, but in Rhizodonium the branches are generally short, often attenuated, 

 and sometimes reduced to unseptate outgrowths (fig. 171 B). The filaments 

 are usually slightly bent and twisted owing to the uneven growth of the 

 individual segments, which are themselves in many cases asymmetrical, and 

 in the vicinity of the branches not infrequently irregular (fig. 171 C). The 

 cell-walls are strong and firm, sometimes conspicuously lamellose, and they 

 may attain a great thickness, as in Rhizodonium profundum and the subaerial 

 species R. crassipellitum (fig. 171 E). 



Fig. 171. A C, parts of filaments of Khizoclonium Berggrenianum Hauck var. Dominicense 

 W. & G. S. West, with short lateral branches, x 450. D, single 'cell ' of E. hieroglyphicum 

 Kiitz. to show reticulate chloroplast and pyrenoids (py). E G, R. crassipellitum W. & 

 G. S. West, a terrestrial species; E, showing great thickness of lamellose wall, x450; 

 F and G, bases of two filaments with rhizoidal outgrowth (;), x 105. 



The nuclei of the segments are greatly reduced in numbers in this sub- 

 family, only two being present in some species of Rhizodonium and in 

 Spongomorpha only one. The chloroplast forms a parietal network in the 

 thicker parts of which pyrenoids are located (fig. 171 D). The reticulation 

 is probably brought about as in Cladophora by the fusion of the produced 

 angles of numerous small plates, each with a pyrenoid. It is sometimes not 

 very obvious, and is best seen in young, actively growing filaments. In the 

 autumn the segments of the thallus are often packed with starch grains, 

 especially in the common freshwater species R. hieroglyphicum. Both Gay 

 ('91) and Wille ('01 B) have described in detail the cytology of certain species 



