Studies on Cyanopliyceae. 93 
collapsed cells, above mentioned, and is consequently no longer 
affected by the Iodine. 
The cyanophycin-granules have formerly been regarded as a 
product of assimilation, comparable to the starch of higher plants. 
Zukal (’94, p, 282) however regarded them as distinctly differentiated 
portions of the protoplasm, although there seems little justification 
for this view (cf. Hieronymus ’92, p. 484); both nitrogen and 
phosphorus have been stated to occur in them. 1 They certainly 
grow during the life of the cell, for those in young cells are small, 
those in older cells and spores much larger. The above assumption 
of the wandering over of the cyanophycin granules into the 
heterocysts requires the existence of a protoplasmic communication 
between the cells of the filament; and I think there can be little 
doubt now that such is the case. Borzi (’86, p. 74 et seq., Tab. III.) 
as far back as 1886 demonstrated such intercellular communications 
between the cells of a Nostoc and an Anabaena. Nadson (’95. 
Tab. V., fig. 55) shows very distinct connections between intercalary 
heterocysts and the adjoining cells in Aplmnizomenon and Tolypothrix, 
Such communications are occasionally to be observed between the 
young heterocysts and the adjoining vegetative cell in the species 
under discussion (fig. 3), and I am also able to give good evidence 
for their existence between the ordinary cells. Figs. 6 and 7 show 
two cases, in which the contents of adjacent spores 2 are being 
liberated in opposite directions and a narrow protoplasmic thread 
connects the two (already widely separated) protoplasts. From 
these and Borzi’s figures it is evident that these intercellular 
communications are far wider that those known in higher plants, 
although an analogy may be found amongst the Thallophytes in the 
Florideae. The width of the communication is such that it would 
admit of the passage of a cyanophycin-granule as an entirety. 
I would therefore regard the heterocyst as a recipient of 
reserve-substances (cf. Hieronymus ’92, Hegler 1901),—as an organ 
for storing up the contents of neighbouring vegetative cells, when 
these, owing to unfavourable external conditions or to active spore- 
formation in the central portion of a filament, become exhausted. 
This quite concords with Hieronymus (’92, p. 483), when he says: 
“Vielleicht haben die Grenzzellen ueberhaupt die Function, 
ubermassig in den vegetativen oder Dauerzellen gebildetes Kyano- 
phycin aufzunehmen und als Speicher fur dasselbe zu dienen.” 
1 cf. Hieronymus ’92, p, 4S9. Wager 1903, p. 405. 
2 The formation of the spores and their germination will form 
the subject of the next paper of this series. 
