Cytology and Movements of the Cyanophycee. 301 
quite visible. InCylindrospermum the division walls thicken 
a trifle at the points where the pore is formed (Fig. 74). 
Sometimes several pores are evident between these cells. 
(5) THe HeEtTeEROcysT. 
Heterocysts, like the spores, are modified vegetative cells. 
The pore, through which the protoplasmic strand passes to 
connect it with other cells, is usually quite large and the 
walls on each side are swollen into decided ridges. Macal- 
lum (49) thought the heterocyst a degenerated cell which 
might be the product of some rudimentary process. Hegler 
(38) called the cyanophycin granules “albuminous crystal- 
loids” and considered that the heterocysts were crowded 
with these, especially at the ends where the pores enter. Borzi 
(6) also considered that the cyanophycin passed into the 
heterocysts through the pores at the ends. The devel- 
opment of the heterocyst of Cylindrospermum has been 
described above. In Wollea saccata and in Nostoc species 
in general the heterocyst is a cell somewhat larger than the 
vegetative cell. In earliest development the nucleus breaks 
up into a thick spireme as if about to divide (Fig. 75), but 
immediately disintegrates, becoming diffused as fine gran- 
ules with here and there a few larger ones (Fig. 76). Dur- 
ing this time there has been passing into the heterocyst 
from the other cells, through the pores, a substance which 
forms a deep staining end to the cell (Figs. 77 and 78), 
when it is stained with iron-ammonia-alum hematoxylin. 
This substance is gradually passed into the heterocyst from 
the adjoining cells on each side until the whole cell is grad- 
ually, but completely filled (Figs. 78 and 79). The sub- 
stance is insoluble in dilute hydrochloric acid (2 per cent.) 
and by digestion in artificial gastric juice. With the latter 
treatment it assumes a golden hue similar to a cell nucleus. 
It would therefore seem to be composed of a substance 
related to chromatin, but this needs further investigation 
