Contributions to Our Knoivledge of the Fresliwater Algae of Africa. 
9 
protococcales. 
(1) CHLOROCOCCACEAE. 
Genus CHLOROCOCCUM Fries. 
1. Chlorococcum sp. (?) (Fig. 1). 
Sample 345 (common). 
This form occurred in the shape of isolated, generally completely 
spherical cells, of rather varying dimensions (diam. 20-36 /x). The wall 
in most cases was moderately thiclr, with a well-defined outer " cuticle," 
but now and again cells were encountered with a much thicker stratified 
membrane (Fig. 1, A). The cell-contents not uncommonly occupied the 
whole interior (Fig. 1, A) ; some of the cells, however, possessed more or 
less contracted contents and, in such cases, one or more oil-drops were 
almost invariably present between the wall and the protoplast (Fig. 1, ^). 
In many of the cells a small spherical body was visible in the middle of 
the protoplast (Fig. 1, A and B). This appeared to be the nucleus, since 
Fig. 1. — Chlorococcum sp. (?). A, cell with thick stratified wall, showing the 
central nucleus (?). B, cell with contracted contents, showing small oil-drops 
and ring of starch near centre of contents, x 650. 
starch was not detected in the immediate vicinity. Pyrenoids seemed to 
be absent, but there was commonly a ring-shaped zone of starch (Fig. 1, jB), 
lying about midway between the surface of the protoplast and the centre 
of the cell. The chloroplast was difficult to decipher, but such indications 
as were obtainable hint at its being spherical. For this reason this form 
is provisionally referred to the genus Ohlorococcum, although in the absence 
of all reproductive stages the reference must remain doubtful. 
(i) HYDRODICTYACEAE. 
Gentjs PEDIASTEUM Meyen. 
1. Pediastrum tetras (Ehrenb.), Ealfs, Ann. and Mag. Nat. Hist., xiv, 
1844, p. 469, PI. XII, fig. 4; Brit. Desm., 1848, p. 182, Tab. XXXI, fig. 1. 
(Syn. : P. ehrenhergii Corda.) 
Samples 311, 312, 327, 345. 
Never very abundant ; 4-8-celled colonies. 
Previously recorded from Cape Colony (Fritsch). 
