272 University of California Publications. [Botany 



solution on the living material is very fine for this purpose, but 

 in many species there are too many other things stained at the 

 same time for one to identify these granules positively. Usually 

 the chromatin is stained blue and the granules red with this stain. 

 An aqueous solution of thionin is also very satisfactory for stain- 

 ing the a granules. It is necessary to over-stain and then wash 

 out with acidulated alcohol. The granules will be the last to dis- 

 appear and these will be stained red. Fig. 14 represents a cell 

 of Oscillatoria margaritifera, killed in potassium iodide-iodine 

 and treated as above described. 



The other, or ft granules, are readily demonstrated with aque- 

 ous solution of wasserblau. The cytoplasm will also take up the 

 stain and obscure the granules, so in order to differentiate them 

 it is necessary to over-stain and wash out with acidulated alcohol, 

 since alcohol alone will not sufficiently dissolve the stain to reveal 

 them. They will be the last to disappear and will stain deep blue. 

 Eosin and picrocarmine will also stain them, but not so satisfac- 

 torily. 



Unlike the a granules (which are always present), the ft gran- 

 ules may be or may not be present in a given species, although 

 in some species they are quite constant. In some collections 

 all of the plants will possess them, in others only certain 

 plants, and still others only certain cells in a filament. Their 

 presence seems to be due to physiological conditions, and in cer- 

 tain cases they seem to have quite a definite relation to the a 

 granules. Thus in a spore formation in the heterocysted group, 

 as the a granules disappear the ft granules increase in number 

 and size. There are indications of this phenomenon in the homo- 

 cysted group. The ft granules seem to increase as the plants go 

 into a resting condition and the a granules seem to diminish. 

 However, my observations on this last point are not sufficient to 

 form a basis for judgment in the matter, but in the case of the 

 spores it is true that the ft granules increase greatly in number 

 and somewhat in size (at times almost completely filling up the 

 spore), while the a granules disappear entirely. The a granules 

 probably give up their material either to form chromatin or to 

 form the ft granules, and the former is more likely since they are 



