Vol. 2] Gardner. — Cytological Studies in Cyanophyceae. 251 



in the middle into the shape of an hour-glass; fourth, the "di- 

 aster ' ' stage, in which the chromosomes are divided in the middle 

 into two groups which move apart, and in favorable cases, spindle 

 fibers are seen in the center of the figure ; fifth, the daughter chro- 

 mosomes arrange themselves parallel to each other and to the 

 long axis of the cell ; and sixth, the union of the daughter chro- 

 mosomes into a daughter spireme. 



To place before the reader the views of Phillips, I quote from 

 his summary of results : — 



1. "The central body of the Cyanophyceae is composed of 

 chromatin and is a true cell nucleus. ' ' 



2. "This nucleus divides by one of two methods, both of 

 which start upon the karyokinetic history, one going no farther 

 than the net-spireme stage, where it constricts itself into halves, 

 while the other continues farther and forms a rudimentary spin- 

 dle with rudimentary chromosomes upon linin threads. 



4. ' ' The chromatin is arranged on the spireme thread in gran- 

 ules which multiply in number by transverse divisions. 



5. "There is no longitudinal splitting of the chromosomes or 

 of the spireme, and in the division of the cell by the method first 

 mentioned above, the two portions of the nucleus are not neces- 

 sarily equal. 



6. "The chromatin is aggregated in hollow vesicles in the 

 resting cell. These vesicles give out their chromatin to the net- 

 spireme very much like the nucleoli of the higher plants, and 

 they may represent it. They are embedded in a granular ground 

 substance. 



7. "The cyanophycin granules and slime balls are probably 

 food products. They are located in the chromatophore. ' ' 



Phillips worked upon "Nostoc (three species), Nostoc in Col- 

 lema, Gloeocapsa polydermatica, Oscillatoria imperator, 0. Froe- 

 lichii, 0. nigra, Cylindrospermum macrospermum, Spermosira 

 litorea, Anabaena flos-aquae, Tolypothrix lanata, Rivularia pi- 

 sum, Gloeotrichia, and Spirulina." 



According to Olive (who has worked upon Phormidium, Os- 

 cillatoria, Nostoc, Cylindrospermum, Calothrix, and Gloeocapsa) , 

 there is a nucleus which divides mitotically. He finds "a more 

 or less dense, fibrous, achromatic portion, and, enclosed by this, 



V OF THE ^ 



UNIVERSITY 



