Notes on the Blue-green Algae, etc. 307 
Tolypothrix, etc. It occurs usually in the peripheral layers 
of the cell, but is sometimes also encountered in the central 
body. The glycogen takes the place of starch, and appears to 
be a product of photosynthesis. It is not found in the absence 
of light or carbon dioxide, and the amount present varies when 
the plants are grown under different coloured light-filters, 
being greatest under orange and red, much less under blue- 
violet, and still less under green-coloured filters. 
Cell division takes place by the formation of a new cell 
wall across the middle of the cell. This begins first of 
all by the formation, on the lateral wall, of a peripheral 
ring, which gradually grows inwards. The cell then increases 
in length, and both central body and. peripheral cytoplasm 
become elongated. As the new cell wall grows it gradually 
brings about a constriction of the cytoplasm and central body, 
until they are finally completely divided into two parts. A 
continuity of protoplasm has been observed in some forms 
from cell to cell, as in higher plants, so that the protoplasts of 
a trichome are all connected with one another. In some cases 
I have observed that prolongations of the central bodies 
themselves are continued from one cell to another, and in 
Cylindrospermum a single deeply-staining strand extends 
through the cell wall from one cell to the next. In many 
cases cell division goes on so rapidly that the daughter cells 
begin to divide before they are fully separated, and in some 
cases a second and even a third division begins before the 
first cell wall is completed. I have observed in one cell as 
many as seven new cell walls in various stages of development. 
Reproduction takes place in the unicellular forms by simple 
division, or by the formation of spores. In the filamentous 
forms reproduction takes place by means of portions of the 
trichome, consisting of one or more cells which become separated 
from the rest and ultimately develop into new trichomes or 
filaments. Sexual methods of reproduction have, so far, not 
been discovered in any members of the group. 
CLASSIFICATION. 
The Blue-green Algz are primarily divided into two orders, 
(1) the Coccogonez, consisting mainly of unicellular plants, 
either free or surrounded by a layer of mucilage derived from 
the cell-wall, and sometimes forming groups or colonies of 
cells in a common mucilaginous matrix, to which such forms 
as Gleocapsa, Chroococcus, Gloeothece, etc., belong, and (2) the 
Hormogoneez, to which the filamentous forms Oscillatoria, 
Phormidium, Lyngbya, Nostoc, etc., belong. 
Some of the filamentous forms are surrounded by a mucil- 
aginous sheath, which is more or less distinctly visible under 
natural conditions; in others the sheath is absent. 
1913 Aug. T. 
