28 



OF THE FREE DIATOMACEjE. 



Fig. 37. 



rapidly, forming a brown layer on the surface of the mud. 

 As soon as a sufficient quantity is produced, the water is 

 carefully poured away, or (preferably in my opinion) is 



drawn off by the aid of a small 

 glass syringe, The mass is now 

 to be swept up with a camel's 

 hair pencil, and either deposited 

 at once on a slip of glass, or im- 

 mersed in clear water. The mud 

 remaining in the plate may be a 

 second time moistened and placed 

 in the sun, and the collection of 

 the Diatomacege repeated as be- 

 fore. By degrees, however, the 

 vitality of the little plants ex- 

 hausts itself, and it is necessary , 

 to revive their vegetative powers. 

 This may be accomplished by 

 creating for them an artificial 

 spring and winter. And there is, 

 in truth, no difficulty in pro- 

 ducing these unseasonable sea- 

 sons ! You have only to allow 

 the water to evaporate, and the 

 mud to become nearly, not quite, 

 dry. Then pour fresh water 

 over it, and once more the Dia- 

 tomaceas break up, and vegeta- 

 tion commences anew. In this 

 way, gatherings originally poor 

 may be made to yield an abun- 

 dant supply of plants. 

 Another contrivance for obtaining the Diatomacese in a 

 pure state is the washing apparatus of Benning, fig. 37. 



It consists of a glass cylinder, two feet six inches in 

 height and two inches wide, on one side of which four 

 holes are pierced, c, d 7 e, /, the lowest at four inches from 



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