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Life-history of Anabaena Cycadeae. 
Anabaena . Examples of this have been seen repeatedly in heterocysts 
of Anabaena Cycadeae and will be described in detail in a later 
paragraph. 
Spores — their Formation and Germination. 
Spore formation in several members of the Cyanophyceae has been 
described by Borzi and Fritsch. This method of reproduction occurs 
abundantly in Anabaena Cycadeae in the algal zone of the nodule, and 
also in hanging-drop cultures under favourable conditions. 
In this species the sporogenous cells are distinguishable by their well- 
marked lateral walls. They usually appear first in portions of the filament 
furthest from the heterocysts. Each protoplast is surrounded by a thin 
strip of colourless substance which assumes a faint brown coloration with 
iodine, and is continuous with the similarly staining intercellular substance 
separating adjacent cells. This constitutes the actual cell membrane, the 
inner investment (Fig. 16, i.if and is bounded laterally by the cell sheath 
(Fig. 16, o. if which maybe a specialized inner portion of the mucilaginous 
envelope (Fig. 16, m . s,) } and becomes more markedly defined as the spores 
develop and the necessity for a firm outer covering arises. The transverse 
limits of the cell sheath gradually become more distinct, and the cells move 
further apart. Eventually the sheath closes round the open ends, envelop- 
ing as it does so a portion of the intercellular septum (Fig. 16). The 
mature spore thus has a complete exospore and endospore (Fig. 16, ex. en.). 
The remaining portion of the intercellular septum swells and separates the 
spores, which in this species are very similar in size and shape to the 
heterocysts. 
The mature spores may rest, but they are also capable of germinating 
immediately under suitable conditions. A large number of germinating 
spores were examined in hanging-drop cultures, where the process could be 
watched in situ in the filaments for any length of time. 
There appear to be four main types of germination. The most 
common is that in which the contents are slowly protruded through a pore 
in the spore wall (Fig. 17). The contents contract, and a colourless papilla 
appears at one side (Fig. 17, b), which advances to the inner investment 
(Fig. 17, c) and then pushes this membrane out in front of the escaping 
protoplast, probably to protect the latter as it passes through the exospore, 
during which passage it is distinctly compressed (Fig. 17, d and e). The 
liberated protoplast is immediately followed by mucilage, which caused its 
liberation, and envelops it before a distinctly differentiated membrane 
appears (Fig. 17,/). 
The second type of germination is that in which a portion of the spore 
membrane is split off (Figs. 18 and 19). The lid so formed may be pushed 
out in front of the exuding mucilage (Fig. 18, a and b ), or it may remain 
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