1899] MICROSCOPiCAL JOURNAL. 8^ 



films of living diatoms on the mud or sands was nearly 

 always on the sunny side and never in the shade, it seem- 

 ed evident that sunlight was necessary to their proper de- 

 velopment, but direct sunlight on a small quantity of 

 water in a warm room would produce a temperature in- 

 jurious if not fatal to the diatoms, and, at the same time 

 favor the development of destructive animals. My con- 

 clusion from observations of many years was that a tem- 

 perature of about 60 F. was the most favorable to suc- 

 cess. Accordingly all the material was placed on an open 

 veranda, exposed to the direct warming sunlight until 

 about ten o'clock, after which it was in partial shade. Af- 

 ter a few hours rest a film of living diatoms had appear- 

 ed on the surface of the sediment in all the receptacles. 



One peculiarity of this film was, that on lifting any 

 part of it, it cohered like a membrane, although it was 

 composed entirely of independent diatoms, all of them 

 rapid travellers. It seemed that in producing their mo- 

 tion they adhered somewhat to whatever substance they 

 were in contact with, thus requiring some force to sepa- 

 rate them from each other, although when a small frag- 

 ment of this film was placed in a drop of water on a slip 

 the diatoms would scatter out in all directions. A piece 

 as large as a pinhead woud fill an inch cell so full in a 

 few minutes that hundreds would appear at a time in the 

 field in any part of the cell. One of the bowls was filled 

 with material taken with a scoop-net from the bottom of 

 a ditch twelve feet wide with water about two feet deep 

 at low tide. This had but a small amount of sediment 

 and contained some Oscillaria and Euglena, and was very 

 rich in Pleurosigma fasciola. The Oscillaria soon col- 

 lected all the sediment into a rounded button at the cen- 

 tre of the bottom leaving the sides of the bowl clean 

 and bare. 



This button of sediment in the early morning was 

 covered with a white substance which in the bright sun- 



