104 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



by the repeated divisions of the cells at right angles to the axis of 

 the cylinder. The form type of such a coenobe is simply a cylinder 

 made up of segments of dimensions characteristic for the species 

 and inherited as qualities of the cells rather than of the colonies 

 as wholes. The disharmony between the numbers produced by 

 repeated cell bipartitions and those required to form stable surface 

 tension figures in one plant does not exist in the case of such 

 simple cylindrical types as are most of the Conjugatae. 



I have described in the present paper only the organization 

 of the eight- and sixteen-celled colonies of P. Boryanuni with 

 the object of suggesting the bearing of the data on the general 

 question of types. The real nature of this organization, both 

 cellular and intercellular, becomes clearer from a study of the 

 method of development and especially the variations in type of 

 both cells and colonies as found in the entire genus. Further 

 observations on these points, as already noted, will be published 

 elsewhere. 



Index of references 



1. Braun, A. Algarum unicellularium genera nova et minus cognita. 



Lipsiae. 1855. 



2. Harper, R. A. Morphogenesis in Pediastrum. Science II. 37: 385. 



7 Mr 1 913. 



3. Meyen, F. J. Beobachtungen iiber einige niedere Algenformen. 



Nova Acta Acad. Caes. Leop. -Carol. 14: 771. 1828. 



4. Nageli, C. Gattungen einzelliger Algen. Zurich. 1849. 



5. . Die neuern Algensysteme. Zurich. 1847. 



6. Nitardy, E. Zur Synonomie von Pediastrum. Beih. Bot. Cen- 



tralbl. 32'-: III. 1914. 



7. Rhumbler, L. Der Aggregatzustand und die iilnsikalischen Be- 



sonderheitcn des lebenden Zellinhaltcs. Zcits. Allg. Physiol. 

 i: 279-388. 1902. 



