BY ARTIFICIAL MEAXS. 241 



1st exper. 2fid exper. ^rd exper. 



The first series has resuhed in the isolation of two species — 

 Achnanthes exilis and Nitzschia linearis. The second, of Cyclo- 

 tella compta and Nitzschia palea. The third — although actuated 

 by an insufficient dilution, although more than fifty out of one 

 hundred macerations employed, and had been fecundated with 

 one or^two diatoms — has yet succeeded in securing in a state of 

 purity Synedra ulva, and a little oval fresh-water Navicula which I 

 have not yet determined. 



You may substitute for the dilution another method that gives 

 good results. It consists in placing a small number of diatoms in 

 a glass containing water, with a layer of gelatinous silica at the 

 bottom. "^The diatoms reach the bottom of the vessel and fix 

 themselves on the gelatinous silica, whence they may be drawn by 

 glass tubes shaped in the lamp to a more or less capillary aperture, 

 and thus transferred to a nutritive maceration. This is only a 

 variation from the former process. 



I have also attempted the separation of diatoms by means of 

 threads (?) placed on fresh gelatinous silica, after the method that 

 Koch employs, to separate the bacteria ; but if by that method 

 you may obtain some Nitzschias, Gomphonemas, or Fragellarias, 

 this modus faciendi is far from being general, the greater part of 

 the diatoms^ not being able to grow upon the silica or in the 

 interior of that substance. Possibly, by resuming these studies, 

 and in consecrating to them a great amount of leisure time, we 

 may come to be able to utilise gelatinised minerals for the separa- 

 tion of the algse that we are studying. However that may be, the 

 old method of division — -fractionnement — is that which at present 

 gives the best results. 



II. — Growth of Diatoms in a State of Absolute Purity. 



In the foregoing cultures we were not specially concerned about 



the separation of the green algae, the fungi, the bacteria, and the 



International Journal of Microscopy and Natural Science. 

 Third Series. Vol. III. R 



