Fritscli, Studies on Cyanophyceae. 
197 
Investment. This by no means does away with the probabilitv 
of interchange between contiguous cells (cf. Fritscli, loc. cit. 
p. 92, 93j, for, §is explained above, I regard the membrane of 
the Cyanojohyceous cell as being of a somewhat plasmic nature, 
and in that-case a gradual diffusion from cell to cell is very 
probable. We might compare a Cyanophyceous hlament with 
a continuons protoplasmic tube, certain portions of which at 
definite intervals are somewliat modified to constitute trans- 
verse septa. 
At the present day we are acquainted with spores or 
resting cells in a considerable number of blne-green algal 
genera and in a recent treatise of Brand’s (03, p. 37) a synopsis 
of the same is given. Yet if we refer to the literatime on the 
subject, — and I abstain from doing so in detail, as Brand 
carefnlly discnsses it in the just-mentioned treatise, — we find 
very little Information as to the mode of development and the ulti- 
mate fate of these spores. In most cases the statements are 
confined to a more or less careful description of the fully matnre 
spore. Borzi practically alone in his ‘Note alla morfologia e 
hiologia delle Alghe ficochromacee , (78, p. 257) enters into the 
subject in somewhat great er detail. His description of the deve¬ 
lopment of the spores in Anabaena FIos-Aquae Ktz. is as follows 
(loc. cit. p. 260): „As in Nostoc the spores are metamorphoses 
of the more internal vegetative cells of each thread. 
This transformation is manifested in the first place by a slight 
increase hi volume of the cell, destined to be changed into a 
spore. Its contents become by degrees finely granulär, wliilst 
the wall grows more and more in thickness. The matnre spores 
have a globose or ovoid form; they are double the size, — or 
a little larger — than the normal vegetative segments, are more 
or less intensely bright yellowish-gold in coloim and are filled 
with innumerable small granules, which lodine tincture stains 
blue. The exosporium is much thicker than the endosporium 
and is provided with very delicate and scarcely disthict ridges". 
I have mainly studied the development of the spores in the 
species of Anabaena r ), whose general features were already des- 
cribed in the first paper of this series (Fritsch 04); but tlieir 
development is so closely connected with the features of the 
cellular investment, that I propose in tlie following to describe 
the two phenomena side by side. Filaments, which are going 
to develop spores, show some signs of this tendency at a rela- 
9 Tliere seems good evidence for this species being Anabaena Azollae. 
Large quantities of the same Alga have arisen in a vessel, containing 
Azolla , which was collected in Brittany last April, and in this material 
lieterocysts are also qnite abundant (cf. Fritsch 04, p. 89. foot-note 2). 
14 
Beihefte Bot. Centralhl. Bd. XVID. Abt. I. Heft 2. 
