226 
F. E. Fritsch. 
me a result of arrested spore-formation, in which owing to some 
unknown conditions the sporogenous cells ceased to increase in 
size, whilst their contents contracted slightly away from the cell- 
membrane and became enveloped by a new (and generally quite 
thick) wall of their own. The conditions under which these 
gonidia developed were certainly not very favourable, for the 
material merely had a thin layer of water, covering the base of the 
containing glass vessel, to exist on ; most of the cells however 
looked quite healthy. This may possibly indicate the way in which 
gonidia-formation resulted from spore-formation, i.e. as an arrested 
stage in the development of the latter. In some of the other forms 
( e.g . Brand’s Phormidium) the power of spore-formation has become 
entirely lost, which may possibly be a result of the development 
of a coherent cell-sheath or may be due to other conditions. 
In concluding it may be as well to briefly summarise the 
essential points in the present paper :— 
(i.) The spores of Anabaena exhibit two main types of ger¬ 
mination, in which the contents are either protruded from the 
ruptured spore-membrane by the formation of mucilage (probably) 
from the protoplast; or, in which the spore-membrane itself becomes 
mucilaginous, whilst the contents retain their original position in 
the thread. 
(ii.) The gonidia of Anabaena are formed by rejuvenescence 
and are surrounded by a well-marked membrane (of two layers) 
before liberation. Their liberation takes place by two methods, 
recalling those of spore-germination. 
(iii.) There is evidence to show that the spores can germinate 
immediately on maturity, whilst the liberated gonidia seem to 
pass through a resting period. 
University College, London. 
November 26tli, 1904. 
DESCRIPTION OF FIGURES ON PLATE VII.. 
Illustratixg F. E. Fritsch’s Paper, “ Studies on Cyanophyceae.”' 
[All the figures refer to Anabaena Azollce, Strasburger, and were 
prepared with an Abbe drawing apparatus. Magnifications:— 
Fig. 1 x 640 ; Figs. 2 to 9, 11 to 14, 20, 26, x 680 ; Figs. 10, 
15, 25, x 850 ; Figs. 16, 19, 21 to 24, 27 to 29, x 1500 ; Figs. 
17, 18, x 600J. 
Fig. 1. Small portion of a filament, showing four spores in the lowest of which 
the spore-membrane is becoming mucilaginous and the contents have 
