IV. 



LIST OF DIATOMS FROM GRANVILLE, OHIO. 



BY J. L. DEMING. 



Diatoms are microscopic unicellular alg^e. Though they were for- 

 merly regarded as belonging to the lower orders of the animal king- 

 dom, microscopists are now agreed in placing them among the Plantae. 

 They are generally of a brown color, though frequently becoming 

 greenish when dry. The endochrome, as the colored contents of the 

 valves are called, is always symmetrically arranged. Each cell is com- 

 posed of two similar and apparently parallel portions, the valves. 



These valves, although nearly equal in length, are not of the 

 same width ; in fact they differ greatly. In consequence of the fine 

 striations and other markings of the silicious valves, they constitute 

 valuable tests of the value of microscopic objectives. 



Diatoms may be often seen to move a little in the water or slime 

 in which they exist. This is especially so in the case of the more 

 elongated forms and for this reason they were regarded as having an 

 animal nature; but it is now no longer believed to be so any more 

 than in the case of the moving vegetable zoospores. There are many 

 theories concerning the movements of Diatoms, but the most plausi- 

 ble one to me is, that heir motion is due to the process of imbibing 

 and emitting fluids in process of their vegetable life. 



Diatoms may exist as individuals, singly or in loose families; 

 they are free or attached to other objects by little stipes, and are fre- 

 quently imbedded in a mucous secretion. The free forms are loco- 

 motive and may be seen in constant motion under the microscope. 



In the process of reproduction they bear a close resemblance to 

 to the Desmids. They increase by division (whence the name from 



