F X- i t s c li , Studies oii Cyanophy ceae. 107 



Investment. Tliis by no means does away witli tlie probability 

 of interchange between contiguons cells (cf. Fritsch, loc. cit. 

 \). 92, 93j, for, as explained above, I regard the membrane of 

 The Cyanoplnjceoitü cell as being of a somewhat plasmic nature, 

 and in tliat case a gradual dil'fusion fiom cell to cell is veiy 

 j)robable. We miglit compare a Cyanop/tyceous lilanient witli 

 a continuous protoplasmic tube, certain portions of wliicli at 

 delinite intervals are somewhat modified to constitute trans- 

 verse septa. 



At the present chiy we are acquainted with spores or 

 resting cells in a considerable number of blue-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 literature on the 

 subject, — and I abstain from doing so in detail, as Brand 

 carefully discusses it in the just-mentioned treatise, — we find 

 very little information as to the mode of development and the ulti- 

 mate fate of tliese spores. In most cases the statements are 

 confined to a more or less carefiil description of the fully mature 

 spore. Borzi practically alone in his "Note alla morfologia e 

 biologia delle Alglie ficochromacee' (78. p. 257) enters into the 

 subject in somew^hat greater detail. Bus description of the deve- 

 lopment of the spores in Änahaena Flos-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 in volmne of the cell, destined to be changed into a 

 spore. Its Contents become by degrees finely granulär, whilst 

 the wall gi'ows more and more in thickness. The mature spores 

 have a sflobose or ovoid form: thev are double the size, — or 

 a little larger — than the normal vegetative segments, are more 

 or less intensely bright yellowish-gold in colom- and are filled 

 witli iimumerable small granules, wliich lodine tinctm-e stains 

 blue. The exosporium is much thicker than the endosporium 

 and is provided with voiy delicate and scarcely distinct ridges". 



1 havo mainly studied the development of the spores in the 

 species of Änabaona \), whose general features were already des- 

 cribed in the first paper of this series (Fritsch 04); but their 

 development is so closely connected with the features of tlu^ 

 cellular Investment, that I propose in the following to describe 

 the two phcnomena side by side. Filaments, whicli are going 

 to devolop spores, show some signs of this tendency at a rela- 



1) There seems good evideuce for tliis species beiug Änahaena Azollae. 

 litirm-c qiiaiitities of the same Alga have arisen in a ves^sel , coiitaiiiin«;- 

 Azolla, whicii was collected in Brittany last April, and in this niaterial 

 heterocysts are also quite abundant (cf. Fritsch 04, p. 89, foot-note 2). 



Beihefte Bot. Centralbl. Bd. XVllI. .\bt. 1. H.lt J. 1^ 



