Studies on Cyanophyceae. 
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F. E. Fritsch, B. Sc., Pli. D., F. L. S 
University College, London. 
II. Structure of tlie Investment and spore-development in some 
Cyanophyceae. 
(Witli Plate VII.) 
1. General remarks. 
In tlie conrse of tlie examination of stainecl filaments of tlie 
Anabaena , whicli formed tlie subject of tlie first paper of this 
series (Fritsch 04), my attention was attracted by the cnrions 
structure, presented by the immediate cellular Investment. The 
detailed structure seenred to indicate, that the cells of a filament 
of Anabaena retain their individuality to a greater extent, than 
appears at first, and although this structure is most emphasized 
in filaments, wliich are proceeding to form spores, it occurs also 
in the purely vegetative stage. A number of furtlier genera of 
Cyanophyceae were examined and the Interpretation of the 
features there observed in tlie light of those, discovered in 
Anabaena, leads to some interesting comparisons; a large number 
of genera still remain univestigated, but I liave purposely 
omitted the more elaborate heterocystous forms for the present. 
The immediate investment of the Cyanophyceous cell lias 
received little attention and those, who have examined it, came 
to very varying results. Like the cell-contents the cellular 
envelope of the blue-green Algae differs very markedly from 
the same structure in other Algae. In tlie first place (and this 
applies to Anabaena amongst others) it is often extremely dif- 
ficult to recognise in the unstained vegetative condition. This 
led some observers such as Kützing (43, p. 48 and 180) and 
Borzi (86, p. 82) to consider, that tlie protoplast was merely 
bounded by a plasmic membrane in most cases; thus within the 
mucilaginous investment of a Nostoc Borzi distinguislies a 
furtlier envelope (’parete*), but this is regarded as being merely 
a peripheral portion of tlie protoplasm (’tutto inseparabile dal 
