Contributio7is to Our Knowledge of the Freshwater Algae of Africa. 55 
scalariform conjugation often occurring in different parts of tliesame thread 
(Fig. 24, A). Lateral conjugation, among the species of the section 
Zygogonium, has hitherto only been observed in Z. rhynchonema, Hansg., 
which is a smaller species with more elongated cells. The zygospores 
Fig. 25. — A-G, Zygnema cyanotpermum, Cleve, forma. A, filament with zygo- 
spores. B, ordinary vegetative cells. C, probable resting stage. D-H, 
Zygnema pectinatum (Vauch.), Ag. (?), akinete-formation. _D and threads 
with mature akinetes, in H in process of splitting apart. E, F, separate 
akinetes. G, part of a filament at an early stage in akinete-formation. A-C 
and E-G x 220 ; D and S x 110. 
formed by lateral conjugation were either of the normal shape (Fig. 24, A)^ 
or often somewhat curved and almost Iddney-shaped (Fig. 24, J5). 
Sample 36 contained abundant stages of a Zygnema forming akinetes* 
* Z. africanum, n. sp., in litteris. It should be mentioned that these akinetes are 
altogether different from those described by De Bary for Zygnema pectinatum (cf. De 
Bary, Unters. Ueb. d. Familie der Conjugaten, 1858, pp. 9, 10, t. 1, figs. 15, 16), so that 
the possibility of their belonging to another species must be borne in mind. 
