No. 466.] STUDIES ON PLANT CELL. VIII. 707 



Olive's results in studies on the Cyanophycese it does not 

 seem unreasonable to hope that more accurate staining of very 

 thin sections will bring the peculiarities of these accounts into 

 harmony with mitotic phenomena of higher forms. 



The accounts of conjugation in yeasts (Barker, :oi and 

 .Guilliermond, 103) which were discussed under "Asexual Cell 

 Unions and Nuclear Fusions " in Section IV give no additional 

 information on the essential structure of the yeast cell. 



2. COMPARISONS OF THE STRUCTURE OF SOME HIGHER TYPES 

 OF PLANT CELL WITH SIMPLER CONDITIONS. 



Some of the most fruitful and interesting fields of investiga- 

 tion in cell structure are likely to be in those border groups 

 between the very simplest conditions of the lower algae and 

 fungi and the higher regions where the nucleus and processes of 

 mitosis have clearly the essential features which are generally 

 ascribed to this structure and its activities. At present the gap 

 seems very great between the simple conditions of the Schizo- 

 phyta and the groups of algae and fungi on the next higher 

 general level. But as a matter of fact we know almost noth- 

 ing of the nuclear structure in the lowest groups of the Chloro- 

 phyceae, i. e., among the simplest of the unicellular green algae. 

 It is rather remarkable that this region should have been 

 so neglected. 



The Nucleus. Comparative studies on the nucleus naturally 

 treat chiefly of the chromosomes and nucleolus. One of the 

 most interesting features of more recent research on the nucleus 

 has been the steady accumulation of evidence indicating that the 

 nucleolus holds a very important relation to the chromatin con- 

 tent. There are types among the lower algae in which the whole 

 or a greater part of the chromatin is gathered into a dense nu- 

 cleolar body in the resting nucleus. Spirogyra is the best- 

 known illustration of this condition and has been studied by 

 several investigators. Similar phenomena have been reported 

 by myself in Corallina (Davis, '98), by Golenkin ('99) for 

 Sphaeroplea, and by Wolfe (: 04) for Nemalion. Some nuclei, 

 however, particularly in the higher plants have nucleoli whose 



