366 THE CULTIVATION OF DIATOMS 



Add to the macerations hydro-carbons, sugar, glycerine, alco- 

 hol, salts of organic acids, and the endochrome of yellow Diatoms 

 becomes habitually colourless ; under the influence of some sub- 

 stances it becomes and remains green. It seems in the first case 

 that the soluble hydro-carbonaceous aliments admit of the Diatoms 

 living without chlorophyll ; that is to say, to live in the absence of 

 the obscure substance, which enables vegetables directly to assimi- 

 late the carbon from carbonic acid. 



Thus it is, mainly by the help of saline substances, that you 

 obtain results most worthy of note. It is with the salts of minerals 

 — (chloride of sodium, of potassium, of magnesium, sulphates, 

 alkaline phosphates, alkaline earth, alkaline bicarbonates, etc.) — 

 that you most quickly obtain cultures that I have termed ^'tetra- 

 logical," where the Diatoms lose the usual form, to take others 

 extremely bizarre — without doubt the action of intoxication, or, 

 rather, the loss of the vegetative sense, called by some authors 

 " Folie du noyau. ^^ 



Is it not surprising that a Synedra or a Nitzschia, which has 

 been placed in bi-carbonate of soda or in an excess of sea-salts, 

 provided with valves whose faces are undulated, divide themselves 

 up into oblique sections, thus giving two, three, and four strange 

 forms ; whilst in ordinary macerations, with very rare exceptions, 

 these species re-duplicate themselves with the greatest regularity ? 



Lastly, M. Tempere places before the readers of La Diatomiste 

 the problem, "Are Diatoms of marine or fresh-water origin?" I 

 believe that it would be unsafe to give a direct reply to this 

 question, based on the inspection of the deposits of fossil Diatoms 

 and of the species now Hving on the surface of the globe. I 

 think that the solution of this problem, which has a retrospective 

 interest, will be most effectually reached in the laboratory, for it is 

 easy to measure the progressive effects of saline solutions on the 

 Diatoms, and to follow the acclimitisation of these algae in media 

 more or less charged with salts, or subjected to increasing tem- 

 peratures. Nothing, then, should hinder us from hoping that it 

 will be possible to arrive at last at the production of forms that 

 have never yet existed, and again to see fossil species, by realising 

 the conditions which prevailed during the multiplication of species, 

 actually lost. The re-habiHtation of fossil Diatoms by retrograde 



