274 University of California Publications. [Botany 



tion distinctly, and no counterstain has yet been found that will 

 do this, so I withhold judgment on this point at present. 



In young cells, and in species in which no (3 granules are 

 present, the cytoplasm, when killed with Flemming's solution 

 and stained with Heidenhain's iron haematoxylin, is shown to 

 consist of a regular network of delicate threads. In other species 

 in which there is an abundance of /? granules present, under the 

 above treatment the cytoplasm has the appearance of a definite 

 alveolar structure, because the granules do not stain with the 

 haematoxylin. 



There is usually a thin layer next to the cell-wall which in 

 all cases is much finer in structure than the coarser structure to- 

 ward the center. Figs. 1 to 6 inclusive show the protoplasmic 

 structure in a plane in which no granules are present. 



I have not been able to demonstrate protoplasmic continuity 

 as seen by other workers. I have tried a large series of distinc- 

 tively plasma stains for this purpose without meeting with suc- 

 cess. Ziel's carbol fuchsin is a very energetic and selective stain, 

 and leaves the cell-wall transparent, while the cytoplasm is deeply 

 stained ; yet in no species studied, from the smallest to the largest, 

 have I been able to detect any connective strands of cytoplasm 

 between the cells except in case of dividing cells, in which the 

 ingrowing cross-walls have not yet completely separated the cells. 



The connection between the heterocyst and the vegetative cell 

 or spore may easily be demonstrated with aqueous solution of 

 wasserblau on living material, washed out with acidulated alcohol 

 after over-staining. 



The cytoplasm contains the coloring matters, there being no 

 special differentiation of chromatophore for this purpose. 



IV. THE PRODUCTS OF ASSIMILATION. 



A few tests were made to ascertain what are the products of 

 assimilation. Starch has not been found in any of the species 

 studied. Some authorities state that glycogen is a constant con- 

 stituent of the Cyanophyceae cell as the first product of assimila- 

 tion, while others affirm that it is never present in these plants. 



