W. B. Crow 
84 
fission. It is absent in many forms. Thus in some species of Chroo- 
coccus, of Glceocapsa and of Merismopedia the mature cells are 
spherical and the products of cell-division, when they first appear as 
separate individuals, i.e. on completion of the fissure between them, 
are hemispherical. But in other species of these genera ( e.g. Chr. 
caldariomm Hansg., M. elegans A. Br., Gl. caldariomm Rabenh.) the 
cells often attain a length equal to about twice their width before 
dividing, so that the daughter cells are approximately isodiametric 
when first formed. In still other Chroococcaceae (e.g. Aphanothece spp.) 
the individual cells are cylindrical from the moment of their forma¬ 
tion. Since, as has been stated already, cell-elongation is related to 
the process of cell-division, the production of cylindrical daughter 
cells chiefly occurs in genera where successive planes of cell-division 
are parallel. Here the direction of elongation becomes a fixed axis. 
When amount of growth is great in proportion to the number of 
cell-divisions the cells may reach a considerable length (e.g. five to 
ten times their diameter). In the longer forms of Aphanothece and 
Glceothece the cells generally become curved. The curvature seems to 
be a direct effect of the greater length. For out of thirty-seven 
species of Aphanothece and Glceothece listed in De Toni’s Sylloge 
Algarum six are described as having cells attaining a length greater 
than three times their diameter, and in all of these the cell may be 
curved. But of the thirty-one short-celled types only Glceothece 
lunata W. et G. S. West shows curvature. Examination of collections 
of individual cells of long-celled species of Aphanothece also shows 
that curvature is correlated with length, although in dealing with a 
single species this is not so obvious since a wide range of variation is 
not covered. It would seem, then, that curvature of the cell is not 
of any morphological significance. With bodies of protoplasm un¬ 
provided with any special mechanical support it would, in fact, be 
surprising if the more elongated forms did not frequently exhibit 
bending. 
In the foregoing we have spoken of long-celled species and short- 
celled species. For if collections of cells of any one species of Aphano¬ 
thece, for instance, be taken from one and the same habitat, it is 
found on examination that little or no variation in length occurs 
other than such as may be due directly to diversity in the age of the 
individual cells. It is therefore probable that degree of elongation 
would be of value in classification, if different species were compared 
under similar conditions of growth. 
Before leaving the elongated cell-type reference must be made to 
