30 DARK GREEN SCUM. 



2. The numerous filaments of uniform diameter, destitute 

 of branches. 



3. Study the movements. 



B. THE INDIVIDUAL FILAMENT. Under high 

 power, notice 



1. The structure in detail, as follows : 



a. The rounded extremities of uninjured filaments. 



b. The outline of an uninjured apex, whether attenu- 

 ated or not, and whether bent to one side or 

 straight. 



c. The delicate lines of the partition walls crossing 

 the filament and dividing it into very small 

 cells. 



d. The comparative length and breadth of the 

 cells. 



e. The granular contents, and their distribution in 

 the cell. 1 



/. The delicate colorless sheath to be seen extending 

 beyond the green cells at some torn end of a fila- 

 ment, and on which may sometimes be detected 

 transverse lines indicating the former position of 

 the end walls of the cells. 



2. The turgidity of the cells: notice that 



a. The transverse walls in an uninjured filament are 

 plane, while 



b. The last cell of an injured filament is bulged out- 

 ward, making the outer transverse wall convex, 

 the pressure from within not being counterbal- 

 anced from without. 



3. Draw one or more filaments. 



1 In some species the granules are collected along the partition walls. 



