208 
Fritsch., Studies on Cyaiiophyceae. 
lower cells of tlie filament, tliose situated more apicady liaving lost 
tMs power witli tlieir tendency to develop into kair-cells. Tliis 
differentiation of apex and base of the filament, wliicli tlius also 
finds its expression in tke external sfieatli and is of conrse like- 
wise exkibited by tke strictly basal development of tlie single 
large spore, is also noticeable in reference to tlie immediate 
Investments of tlie cell. In tlie basal cells of a filament tlie 
cell-skeatk is readily visible ontside tlie colomless inner Invest¬ 
ment of eacli protoplast (fig. 10, c. s.); in most filaments it is 
liowever less and less easy to recognise as one advances towards 
tlie apex and tlie cells, wliicli make np tlie liair-like termination 
of tlie filament, are invariably devoid of a cell-slieatli and only 
possess tlie inner investment. As in tlie case of tlie external 
sfieatli, mentioned above, is is very difficnlt to fix tlie precise 
point, at wliicli tlie cell-skeatk is no longer evident, nor is tliis 
point by anv means constant in different filaments: in one case 
tlie great er number of cells of a filament are witliont tlie cell- 
sfieatli, wliilst in anotlier tlie majority is provided witli tliis 
latter investment. Tlie cell-slieatli presents tlie same marked 
mondiform structure, as in tlie filaments of a Tolypothrix and 
for wliole stretclies tlie cell-skeatks of tlie individual cells may 
be quite distinct from one anotlier, as in Anabaena : in sucli 
regions tlie structure of tlie filament is identicad}^ tliat of tliis 
latter genus. O 11 tlie wliole liowever tlie ced-slieatlis are more 
commonly f'ound united, altfiougli sucli a colierent cell-slieatli 
differs from tliat of Oscillaria and agrees witli tliat of a Tohj- 
pothrix. in its very marked mondiform constrictions. 
Tlie single large basal spore develops from a single vege¬ 
tative ced by great increase of size of tlie latter: as develop¬ 
ment proceeds tlie external mucilage at tlie base of tlie filament. 
becomes more and more distinct, and idtimately forms a ratker 
closely-fitting slieatk round tlie mature spore. It is noticeable 
tliat, wkereas tlie ordinary vegetative cells are only stained 
faintly brown by lodine, tke sporogenous cell and often also 
one or two of tlie fodowing cells take on a deep brown colour. 
I liope to be able to furnisk furtker details of tke development 
of tke spores in tliis genus subsequently, but as yet I liave not 
been successful in finding many stages. 
General conclusions. 
In tlie following paragraplis I sliall attempt to put some 
interpretation on tke above-discussed plienomena and endeavour 
to sketcli out tke line. along ivliicli tke filamentous forms deve- 
loped from tlie unicellular. Muck of wkat fodows is not neiv. 
but I consider its recapitidation necessary for a full understan- 
ding of tke facts. 
Tke simplest form, tliat kas been examined, is Gloeocapsa 
and tliere seems no reason to suppose tliat its structure differs 
