F r i t s c li, Stndies 011 CyanopTiyceae. 
195 
corpo protoplasmatico'), and the same conclusion is arrived at in 
the case of Oscillaria. Mucli tlie same view is lield by Bor net 
and Fl ah auIt in tlieir „Revision des Nostocacves heterocystees“ 
(86), where the protoplasm of the cell is considered to he in 
direct contact. with the slieath. Much the most important con- 
tribution on tlie subject is Gromont’s „Reeherches sur les enve- 
loppes cellulaires des Nostocacees hlamenteuses LL . based on the 
examination of 11 genera. Whilst a large part of the paper is 
concerned with the slieath, tlie conclusions arrived at with regard 
to the immediate envelope of the cell are summarised by Gromont 
as follows: „La membrane propre de la cellule est toujours 
mince, etroitement appliquee contre le plasma, mais eile peut 
etre cependant mise en evidence par la dissolution et la con- 
traction de celui-ci; eile est insoluble dans les acides et ne se 
colore jamais en bleu par les reactifs iodes u . Gromont thus 
considers that a definite membrane is present in all cases and 
this view is also adopted by Kirchner (98, p. 46). I refrain 
frorn citing further literature, as Gromont has done so fully up 
to the time of his publication. 
On the grounds of my investigations I liave come to the 
conclusion, that eacli protoplast in the CyanopJiyceae is provided 
with two investments of its own in the mature condition inde- 
pendently of the external mucilaginous slieath; the inner of fliese 
investments forms an actual membrane right round the proto¬ 
plast, whereas the out er takes the form of a small cylindrical 
slieath enveloping the cell. These will be described more fully 
in the course of the detailed consideration of the genera and I wisli 
at this point only to make a few remarks on the nature of the 
inner investment, which corresponds to the celhmembrane of 
the two observers just mentioned. I have already mentioned 
above that it is difhcult to distinguish the immediate envelope 
of the Cyanophyceous cell in many cases; this liowever only 
applies to the lateral portion of this envelope, for adjacent cells 
are separated frorn one another in Anabaena (or Nostoc) by a 
well-marked colourless patch, representing the transverse septum, 
but the lirnits of this latter with reference to the protoplast are 
mostly difhcult to dehne. Gromont (88, p. 209) successfully 
devised a method, by which tlie cell-wall of Cyanophyceae could 
be rendered evident und by means of which he attained tlie 
above-mentioned results; he employed a 83 0 o solution of chromic 
acid, which in the course of an Jour or so dissolves away the 
greater part of the protoplasmic contents, leaving the bell-mem- 
brane perfectly intact, although a slight contraction seerns to 
me to be involved. Here therefore we meet with a second 
peculiarity of the cell-wall of the blue-green Algae, viz. its 
resistance to strong oxidising agents; in this respect it differs 
very markedly frorn most other plant-membranes r ). According 
9 According to Gomont Hoc. eit. p. 212) similar reactions are sliown 
by tlie membranes of some otlier Algae (e. g. a Protococcus, a Conferva, 
and a Cladophora ); tliese membranes are liowever qnite different pliysically. 
