Cytology and Movements of the Cyanophycea. 301 



quite visible. InCylindrospermiim 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 Heterocyst. 



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, yy and 78), 

 when it is stained with iron-ammonia-alum hsematoxylin. 

 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 



