Coccomyxa subellipsoidea, a new member of the 
Palmellaceae. 
BY 
ELIZABETH ACTON, B.Sc. 
University Scholar, Birmingham. 
With Plate XLIIL 
HE Alga which forms the subject of this paper has long required 
1 thorough investigation. It is widely distributed in all parts of the 
British Islands, occurring only in subaerial habitats, generally on damp 
rocks and stones. It forms a thin mucous stratum of a dark green colour, 
which when dry becomes almost black and peels off the stone. The same 
Alga is not infrequently found in cold greenhouses, the green mucous 
stratum occurring both on the glass and woodwork, if sufficiently damp. 
The stratum consists of large numbers of thin-walled cells embedded in 
a colourless mucilage. The cells are not all of precisely the same form, but 
for the most part they could be described as somewhat irregularly or 
obliquely ellipsoid. 1 Among these ellipsoid cells are some in which the ends 
are more pointed, and others which are almost spherical. Sometimes one 
end of the cell is much more pointed than the other, especially after 
division has just taken place. The cells are 6-io/x in length by 4-6/01 in 
breadth. Each cell has a thin inner cellulose wall and an outer gelatinous 
coat. The chloroplast is parietal, and of variable shape, seldom covering more 
than half the cell-wall (PL XLIII, Fig. 1). It sometimes forms a U-shaped 
band and sometimes a shallow cup ; and the margin may be entire, un- 
dulated, or drawn out into fine processes, which occasionally meet across 
the central vacuole (Fig. 1 a). In unstained material no pyrenoid is visible, 
though in some specimens small refractive granules can be distinguished ; 
but on treating with a solution of iodine in potassium iodide a single pyrenoid 
becomes visible in the centre of the chloroplast, while the refractive granules 
are seen to be starch granules. 
1 The form of the cell evidently varies slightly under different conditions. In material collected 
three months later from the same place as that described above, the majority of the cells were 
nearly spherical. 
f Annals of Botany, Vol. XXIII. No. XCII. October, 1909.] 
