Fritsch, Studies 011 Cyanopliyceae. 
203 
At tlie same time young stages of Gloeocapsa are always 
to be found in which the cell-sheath is nnrecognisable and in 
tlnese tlie demonstration of tlie inner investment is a very diffi- 
cult matter; even with tbe lielp of ehromic acid I was not 
able to render it visible in a satisfactory mann er, owing appa- 
rently to tlie very considerable contraction in tliis case. Brand 
lias already (00, p. 4) commented on tliis difficulty, but mentions 
a case, in which „ganz frische Teiliingsproclukte einer Zelle . . 
. abnormer Weise durch eine farblose schlauchähnliche 
Brücke zusammenhingen“, which is probably due to special 
development of tlie inner investment in the case in question: 
I have met with similar 'phenomena (i. e. cases, in which two 
adjacent cells were connected by the much drawn out transverse 
septum) in Anabaena , and in my opinion tliey tend to eonfirm 
the gelatinous nature of the investment. 
Tlie portion of the investment, that I have called the cell- 
sheath in Gloeocapsa , was also recognised by Hägeli (49, p. 47, 
481, for he says: „Die Zellwandung (i. e. the entire investment) 
ist sehr dick und in der Regel das Zelllumen mehrmals tiber- 
treffend, selten demselben bloß gleichkommencl. 
An der Wandung kann meistens die schmale Zellmembran und 
die breite Hühmenibran unterschieden werden“. Hägeli's „Zell¬ 
membran“ corresponds to tlie cell-sheath and the „meistens“ 
indicates, that he already observed its occasional absence; the 
„Hüllmembran“ refers to the external mucilage. Brand (00, 
p. 7) also came to the conclusion, thatHägeli's „Zellmembran“" 
was not the actual cell-membrane, for he says: „jene öfters 
bemerklichen Zonen, welche Hägeli im Auge zu haben scheint, 
gehören aber der Gallerte an, und die eigentliche Zellliaut von 
Gloeocapsa (alpina) ist, wie bereits angedeutet, mit den gewöhn¬ 
lichen Hilfsmitteln überhaupt nicht zur Anschauung zu bringen“. 
In the case of Chroococcus helveticus Ivlebs (86, p. 391) states 
that: „Jede intensiv blaugrüne feinkörnige Zelle besitzt eine 
äußerst zarte, dünne Zellwand“ and here also I have no doubt 
that the cell-sheath is meant. 
When the colonies of a Gloeocapsa or Gloeothece are sub- 
jected to a 33 °o solution of chromic acid tlie externa! stratified 
sheath is first attacked and gradually dissolved away; it takes 
some little time before the acid reaches the cell, but then, as in 
Anabaena , the cell-sheath slowly disappears, unless the cells have 
reached the mature size. The inner investment, as already men- 
tioned, is very difficult to discern afterwards. 
A few words may be added on the genus Merismopedia , 
in which a large number of cells are bound together by thin 
transparent mucilage to form fiat plates; owing to tlie small 
size of the cells specimens, stained with Yesuvin, were examined. 
The cell-sheath in these is well marked in contrast to the inner 
investment: it is either confined to pairs of cells or surrounds 
larger groups of them, when rapid division is taking place. The 
former state of affairs is bv far the commonest and it is noti- 
