Fritsch, Studies on Cyanophyceae. 
209 
from that of tlie related unicellular forms in anv essential 
respects. It is of especial interest because it is one of tlie uni- 
cellular Cyanophyceae , from which tlie higlier filamentons forms 
were in all probability derived. In tliis genus the cells are 
capable of dividing in three directions at right angles to one 
another, and if we suppose, as seems most likely, that the 
ancestor of such unicellular forms was capable of dividing along 
all directions (a parallel for which is found in Aphanocapsa) 
GJoeocapsa represents a fairly primitive type, — more primitive 
probably than a form like Merismopedia , wliicli is only capable 
of division along two directions. If we imagine the capacity 
for division along one of these planes to become lost ( Aphano - 
thece, Gloeothece ), we reach the conditions, necessary for the 
development of the iilanientous stage and witli that pass on to 
the higher 'forms; in correspondence with tliis tendency for 
division solelv along one direction we lind that tlie spherical 
cell of a GJoeocapsa or Merismopedia acquires a more or less 
pronounced cylindrical form (in Gloeothece , etc,). In Gloeothece 
and Aphanothece liowever the fLlamentous tendency is still opposed 
by the consistency of the ellipsoidal or spherical mucilage enve- 
lopes, which effectively prevent the formation of a row of cells 
by tliis uniaxial division. The phenomenon, which we liave 
before us here, is well described by Hägeli (19, p. 57) in the 
following passage: „In der Mutterblase (i. e. the enveloping layer 
of mucilage) liegen die beiden Tochterzellen nach der Teilung 
hintereinander. Sie dehnen sich dann in die Lau re; ist die 
Blase weich, so folgt sie anfänglich dem Drucke, reiht aber, 
wenn die Tochterzellen ihre eigenen Blasen bilden (hg. 2 c). 
Besitzt dagegen die Mutterblase zweier Individuen nicht so viel 
Elastizität, um dem Drucke der Ausdehnung dieser letzteren 
folgen zu können, so werden dieselben mechanisch von der ur¬ 
sprünglichen Richtung ab gelenkt (hg. 2 b ; hg. 3 b, c). Mit dem 
weiteren Wachstum und der Bildung der eigenen Hüllmembranen 
weichen sie zuletzt so sehr von der anfänglichen Stellung ab, 
daß sie mehr oder weniger parallel neben einander liegen 
(hg. 3d, e). a — The same applies to Aphanothece. — In the 
genus Synechococcus we have a, stage, which takes us onwards 
a little way towards tlie iilamentous series. As in Aphanothece 
und Gloeothece we have cylindrical cells, dividing in one direction 
only, but the colonies are only surrounded by a loose diffhient 
mucilage. As a rule division apparently follows the lines of 
that in GJoeocapsa , Gloeothece etc., mucilage being formed abun- 
dantly between the products of division and the cell-sheath no 
doubt forming a complete envelope round eacli individual cell: 
occasionally however the int er cellular mucilage is less developed 
and the products of division form short rows of cells. It remains 
to be seen whether tlie cell-sheath is then individual to eacli 
cell or coherent. I have not been able to obtain Synechococcus 
for this Investigation, but judging from memory and the publislied 
figures, it seems probable that the form#? will be the case. The 
