FRESHWATER PLANKTON ALCLE FROM CEYLON 
139 
those of some species of Microcystis, from which they can be dis¬ 
tinguished by the absence of pseudo vacuoles or, in the case of 
3L. marginata , by their more indefinite outline. A. Grevillei is not 
usually a free-tloating species, although W. & G. S. West found a 
plankton variety of it at JBallinah.inch, Ireland, whilst more recently 
Gl. M. Smith found it as a facultative planktont in Wisconsin. The 
Ceylon specimens were evidently free-floating colonies, slightly ellip¬ 
soidal, averaging about 80 g long and 70 g wide. The determination 
in the case of the second localitv mentioned below is doubtful, on 
*/ * 
account of the lack of colour in the material. Here it was found 
amongst floating algae and in bluish-green scum at some points near 
the margin. JLoc. 2, 9. Distr. Eur., N. Amer. 
A. eelicatissima W. & G. S. West. The cells were appreciably 
blue-green in the collections from the localities recorded below. A 
similar organism occurs in several of the other specimen-tubes, but as 
in these the cells are at present colourless, it is quite likely that 
they may have belonged to bacteria. Such bacterial groups are 
not rare in the plankton. The significance of the discovery of blue- 
green algae of bacterial size has been commented on by G. M. Smith 
(Wisconsin Phytoplankton, 20). Cells 5 g-7’5 g diam. JLoc. 3, 10. 
Distr. Eur., N. Amer. 
Apiianotiiece Naeg. 
No true plankton species observed. 
A. stagnina (Spreng.) A. Br. The reproduction of the colonies 
takes place by vegetative breaking of the mucilage masses. The 
products of this are presumably the microscopic spherical masses of 
varying size which were fairly numerous. All stages were seen 
from these microscopic spherical masses to large irregular macroscopic 
masses. In the limited material at our disposal the largest were 
about 4 mm. in length, although this species is stated to attain the 
size of a walnut. JLoc. 11. Distr. Eur., N. Amer. 
Microcystis Kuetz. 
As far as our observations go, the members of this genus would 
appear to be by far the most important constituents of the freshwater 
phytoplankton of Ceylon at the period when the collections were 
made. A description of the new species observed and a study of the 
classification of the genus is published elsewhere (New Phyt. 1923, 
no. 2). 
M. aeruginosa Kuetz. Loc. 4, 7, 9, 12, 13. Distr. Eur., 
N. Amer., Centr. Afr., Madagascar, Ceylon. 
M. flos-aqlle (Wittr.) Kirchner. Loc. 2, 14, 15, 10 (water- 
bloom), 17, 18. Distr. Eur., N. Amer., Centr. Afr. 
M. protocystis Crow. Loc. 0, 9 and 10 (water-bloom), 18, 19. 
M. pseudofilamentosa Crow. Loc. 20. 
M. marginata (Menegh.) Kuetz. Loc. 3 (rare), 4 (rare), 19. 
Distr. Eur., N. Amer. 
M. viRLDis (A. Br.) Lemm. Loc. 3. Distr. Eur., Centr. Afr. 
M. holsatica Lemm. Loc. 0. Distr. Europe. 
