lis THE AMERICAN MONTHLY [April 



Some Experiments on the Growtb of Diatoms. 



By GEORGE C. WHIl'PU:. 



NEWTON CENTRE. MASS. 



In a paper publislied in 1894 tlie writer suggested an 

 explanation for the peculiar seasonal distribution of 

 diatoms in hikes and ponds. It was shown that in deep 

 ponds these minute plants are found abundantly during 

 the spring and fall, but are almost entirely absent during 

 the summer and winter; that these growths are closely 

 connected with the phenomena of circulation and stagna- 

 tion of the water, which phenomena are due to tem- 

 perature changes; and that it is during the periods of the 

 year when the water is in complete circulation through- 

 out the vertical that the diatom growths occur. The ex- 

 planation offered for these facts had reference chiefly to 

 the food supply. It was stated that diatoms require a 

 suflBcient supply of nitrogen in the form of nitrates, and 

 that they require a free circulation of air, and it was 

 shown how during the "periods of circulation" in tlie 

 spring and fall these conditions were fulfilled. In the 

 light of more extended observations and experiments this 

 food supply theory, taken alone, is seen to be inadequate, 

 and while it is true that the question of f()od is one of 

 fundamental importance, yet there are other factors 

 which materially influence their growth. With a view 

 to determining the nature and effect of some of these in- 

 fluences the writer has conducted recently several series 

 of experiments, some of the results of which are here 

 presented. 



It is not an easy matter to cultivate diatoms success- 

 fully in the laboratory to obtain comparative results. 

 They are organisms which have an extremely sensitive 

 nature, and slight changes in their environment often 

 make great differences in their growth. The tempera- 

 ture, the amount of light, the shape and size of the jar 

 in which they are grown, the action of the glass upon the 



