322 Mr. J. Ralfs on the Nostochinee. 
or cells are commonly more or less orbicular, but sometimes dis- 
ciform or cylindrical, and in a few instances confluent. At first 
they are uniform ; they divide in the same way as they do in 
other simple Algz, and during division are geminate. 
I beheve that the filaments multiply in consequence of the 
division of the jomts being here and there complete in the same 
way as in Oscillatoria ; because we find that the filaments im 
an early state (as Mr. Hassall has correctly noticed) are but spa- 
ringly scattered through the mass, whereas in mature specimens 
they become very numerous. Mr. Hassall considers that this 
merease results from the separation or dislocation of the enlarged 
cells. I believe, on the contrary, that when the enlarged cells 
are fully formed the plant approaches maturity, and the filaments 
cease to multiply. The following facts will, I think, prove that 
the multiplication of the cells has no essential connection with 
the enlarged jomts. In Cylindrospermum they terminate the 
filament, vet here the filaments are as numerous as in the other 
genera, nor do we find them of more unequal lengths, which 
would however necessarily be the case if the enlarged terminal 
joints separated to form new filaments ; and further, the enlarged 
joints themselves are not developed until after the filaments have 
become numerous. 
As I have stated above, the joints or cells are at first uniform 
in size and figure; but in the mature plant they are of three 
different kinds, all of which are generally, though not I believe 
imvariably, present in the same filament. These are— 
Ist. Ordinary joints or cells —Of these I shall only observe, 
that they divide by separating into two hemispheres, each gra- 
dually acquirmg a new portion in the room of that from which 
it has separated, and that until this process is complete they ap- 
pear geminate. As this geminate state is common to every spe- 
cies during growth, it cannot be employed as a specific character, | 
and as the other cells do not divide, the elongation of the fila- 
ment must be solely due to the ordinary ones. Their endo- 
chromes are slightly granular, which gives them a dotted ap- 
pearance. 
2nd. Vesicular joints or cells*.—These make their appearance 
at an early period. They are generally orbicular, but sometimes 
elliptic, and are usually larger than the ordinary cells. They are 
evidently analogous to the vesicles present in Rivularia and in 
some of the Oscillatoriee. They do not contain granular matter, 
but are filled with a bluish fluid, which eventually acquires a brown 
tint. When mature they are frequently furnished with diverging 
hairs or cilia. They seem to be connected with the adjacent 
* By Mr. Thwaites they are named, from their usual position, ‘ connect- 
ing cells;’’ they have also been called “ Heterocysts.” 
