Contributions to Our Knowledge of the Freshwater Algae of Africa. 49 
of diiference, viz. the threads are wider, the end-walls are not folded, there 
appear to be constantly three or four chloroplasts showing either a number 
of turns or, more rarely, running almost longitudinally, the fructifying cells 
are often not inflated, and, when inflation occurs, it is very slight, and the 
membrane of the zygospore is much thicker. 
E^iG. 21. — Spirogyra subreticulata, F. E. Fritsch, n. sp. A and I, portions of 
two vegetative filaments showing the varying disposition of the chloroplasts 
and the thick septa. £, C and F, threads with zygospores. D, part of a 
zygospore, on a large scale, in optical section to show the structure of the 
wall. E, surface-view of a small portion of the wall showing the reticulation 
of the middle layer. G and H, extreme forms of zygospores. A, B and 
I X 260 ; C and P x 90 ; D x 430 ; jB x 860 ; 6? and H x 170. 
The zygospores are rather variable as regards relation of length to 
breadth and also in respect of their shape. Extreme forms are shown 
in Fig. 21, G and H, but most commonly they are elliptical, often with 
somewhat pointed ends (Fig. 21, C and F). The very thick zygospore- 
membrane is composed of three distinct layers (Fig. 21, D) ; there may 
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