152 ON THE CULTIVATION OF DIATOMS 



by the gradual blackening of the protoplasm of the cellules, at 

 the end of the disease the contents of the frustules becomes 

 grey, but in the dead cellules the shrivelled endochrome becomes 

 as black as coal. The chapter relating to the diseases of Diatoms 

 under artificial culture is therefore very extensive, and the 

 diatomist must expect numerous infections, very varied in their 

 manifestation, and which may come altogether unforeseen, to 

 neutralise his operations. 



Hitherto we have only spoken of the cultivation of Diatoms 

 by daylight, which is uneven and variable in its action. To avoid 

 the irregularities of the natural light, I have tried, and succeeded, 

 in growing these algae by gas-light. The flame of a jet burning 

 from 50 to 100 cm. of gas per hour, is sufficiently life-giving to 

 promote, at a distance of o'2o cm., the growth of the greater part 

 of the marine and fresh-water Diatoms. You can even obtain 

 splendid growths of Melosira and Fragillaria, which fill all the 

 liquid, giving magnificent tufts, formed by an infinity of yellow 

 filaments, perfectly endochromed. Nearly all the marine and 

 fresh-water Diatoms, as I have said, develop under the action of 

 gas-light, and I have no want of success to notice, even in the 

 growth of the marine Pleurosigmas, the cultivation of which is a 

 most delicate affair. 



When the artificial light, is feeble, as when 40 to 50 litres of 

 gas are burnt in an hour, many of the Diatoms that are mobile in 

 daylight increase and multiply, without sensible movement, but as 

 soon as, and in proportion as the light is increased, they are seen 

 to regain their habitual movements, even when their length is 

 greatest, as certain Naviculas, Pleurosigma Balticum, Cymato- 

 pleura solea, the long Synedras, etc. 



The apparatus that M. Admet, of Paris, has constructed for 

 me, for the growth at the same time of a great number of Diatoms, 

 is represented in PI. VIII., Fig. 2. It is composed essentially of a 

 cylindrical chamber, capped with a conical cover, E, surmounted 

 by a chimney that draws off the products of combustion. The 

 vertical division and the lower part of the chamber are furnished 

 with a double envelope, that allows a current of cold water to 

 circulate around them, and thereby to lower the temperature of 

 the growths when they are acted on by very intense luminous rays. 



