Diatoms 



113 



Its cells are very small, and easily overlooked, since 

 they largely escape the finest nets and are only to be 



Fig. 36. A nearly pure culture of IMeridion, showing colonies of 



various sizes. 



gathered from the water by filtering. Often, however, 

 their abundance compensates for their size. Kofoid 

 found their average number in the waters of the Illinois 



