696 THE AMERICAN NATURALIST. [Vol. XXXIX. 



try to give the present status of investigations in these most 

 difficult subjects. 



Cyanophycea {Blue-green- Algcs). — The most recent and com- 

 prehensive papers on the cell structure of the Cyanophycese are 

 by Fischer ('97), Macallum ('99), Hegler (:oi), Butschli (:02), 

 Kohl (: 03), Zacharias (:oo, :03), and Olive (:o4). Olive gives 

 an especially clear analysis of the situation in this field of 

 investigation at the present time and an excellent historical 

 review of earlier literature may be found in Hegler (:oi). The 

 discussions center chiefly around (r) the presence or absence of 

 a nuclear structure and its behavior in cell division, (2) the dis- 

 tribution of the blue-green pigment (phycocyan) and the struc- 

 ture of a possible chromatophore, and (3) the nature of certain 

 conspicuous inclusions within the cell, called cyanophycin gran- 

 ules and slime globules. An outline in tabular form of the 

 views of some thirty investigators on these subjects is given by 

 Ohve (:04, p. 10). 



Writers from the earliest periods of cell studies on the Cyan- 

 ophycese have recognized the presence of a central body in the 

 interior of the cell more or less sharply differentiated from the 

 peripheral region, which holds the coloring matter and certain 

 inclusions. The central body contains granular material which 

 stains and behaves in other particulars lilce chromatin. But as 

 a rule this granular material is not confined within a membrane 

 or vacuolar cavity which has proved the most serious difficulty 

 to its acceptance as chromatin and the central body as a nucleus. 

 Then many investigators have not been able to satisfy them- 

 selves that the central body exhibits the phenomena character- 

 istic of nuclear division even in a simple form. Consequently 

 much doubt has been expressed as to its morphology and pos- 

 sible relation to a nucleus. 



The most recent and detailed investigations have, however, 

 brought forward much evidence to the effect that the granular 

 material in the central body is chromatin which becomes organ- 

 ized into chromosomes that are distributed by a form of mitotic 

 division. In the vegetative cells, which generally divide rapidly, 

 the chromatin is never held within a nuclear membrane but in 

 young heterocysts and spores such inclosing membranes have 

 been found (Olive, : 04). 



