The Freshwater Algae of Africa. 533 



evidently varying development of t lie creeping base and of the upright 



system. I have been unable, however, to convince myself that the 

 present form belongs to any of the species hitherto described, and I 

 am therefore led to add one more to the already long list of species of 

 this genus. 



Stigeoclonium prostratum,* us the specific name indicates, is one of 

 those species in which the creeping base is very strongly developed, at 

 the expense of the upright system. The base, which appears to be 

 purely epiphytic, forms a very extensive and richly branched system, 

 readily seen on the surface of the substratum with a magnifying glass. 

 1 11 general the branches, although very close to one another (Fijj,-. 1 7, B), 

 are nevertheless quite distinct, but at some points the branching is so 

 dense that a one-layered parenchymatous stratum arises (Fig. 17, A), 

 an apparently rather unusual condition. In parts of the branched 

 base the ramification is very distinctly unilateral (Fig. 17, B), one 

 branch, but apparently not more than one, arising from almost every 

 cell of the main axes. The secondary branches are short and, at the 

 best, bear but short (often only one- or two-celled) branches of the 

 third order (cf. Fig. 17, 7?). 



The upright system is very scantily developed and takes two forms. 

 At certain points, where the creeping base is more laxly branched, 

 numerous short, 1-5-celled (commonly 3-celled) branchlets arise in a 

 semi-radial manner, projecting in all directions from the substratum 

 (Fig. 17, C). These points of development of upright branchlets occur 

 at wide intervals, sepai'ated by long stretches in which the base is 

 purely procumbent. The upright branchlets are more or less pointed 

 at the ends, but I have never observed them to be drawn out into a 

 hair, nor are they, as far as I have seen, ever branched (cf. Fig. 17, C). 

 The second form taken by the upright system is that of simple hairs, 

 often of very considerable length (more than 400 /x in some cases). 

 These hairs arise at quite irregular intervals from the creeping base, 

 often have a slight basal inflation, and ai-e provided with very scanty 

 contents (Fig. 17, B, D). In many cases they are septate, but I have 

 been unable to convince myself that this is always the case. In part 

 they arc drawn out into a point (Fig. 17, B), in part they have a 

 blunt termination (Fig. 17, D). 



The cells of the creeping portion are in general rectangular in shape, 

 whilst in section they either appear elongated parallel to the sub- 

 stratum, or their outer wall is more or less convexly arched (Fig. 17, 

 B, D) ; where a parenchymatous disc is formed, the shape of the 



* Referred to under the name of Myxonema prostratum in New Phytol., xv, 

 1916, p. 236, fig. 1, e. 



