Studies on Cyanophyceae. 221 
not undergo division until fully liberated, but this is not invariably 
the case. 
In the second type of germination the exospore itself becomes 
mucilaginous—possibly the endospore also—and gradually swells up r 
its outer circumference increasing more and more in extent; in this 
way the contents of the spore, whilst retaining their original position 
in the thread, come to be surrounded by a thick zone of colourless 
mucilage, which may be stratified or not (Figs. 1, 2, 9, 13 and 14). 
Frequently when several spores, lying side by side behave in this 
way the enveloping mucilage becomes more or less confluent (Figs. 
2, 11 and lower part of 13). The contents of the spore may begin 
to divide very soon after the transformation of the exospore 
commences (cf. Figs. 1, 11 and 13), although just as frequently the 
division of the contents is postponed until the mucilaginous envelope 
has attained considerable dimensions (Fig. 4). In this type of 
germination a well-marked wall generally becomes apparent round 
the contents at an early stage. In many cases the whole wall of the 
spore does not become mucilaginous, but some portions of it remain 
unaltered (cf. Figs. 5, 6 and 8); we may regard this as a combi¬ 
nation of the two main types of germination. Such cases often 
resemble those in which the membrane is widely opened by the 
escaping mucilage in the first type of germination. On the whole 
the first type of germination and its variations are more frequently 
met with. 
The germination of the contents of the spores may (in both 
of the above types) take place in various directions, most commonly 
in the direction of the axis of the filament (Figs. 1, 2, 7, 9 and 13); 
not rarely, however, the axis of the new filament is perpendicular 
(Figs. 14 and 10 at l), or oblique (Fig. 8) to that of the mother 
filament. This appears to depend on the mode of opening of the 
spores and indirectly on those influences, which lead to this latter 
phenomenon (cf. p. 220). Heterocysts began to develop in the young 
chains at a very early stage, a 3-celled filament not uncommonly 
having one (rarely two) of its cells transformed into these structures 
(cf. Figs. 7, 8 and 9); the young plant thus even at this stage mani¬ 
fests the tendency towards the production of heterocysts, so 
prevalent in the mature filaments (cf. Fritsch, loc. cit. p. 89). The 
extreme case is attained, when the contents of the spore on 
liberation develop into a single heterocyst,—a very rare phenomenon, 
which appeared to be the result of germination of dwarf-spores 
with very few contents. These points again suggest a number of 
