HARDWI CKE ' S S CIE NCE-GO SSI P. 



241 



THE NATURAL HISTORY OF DIATOMS. 



■AITH the title of 

 " The Diatoms of 

 the Alps and the 

 Jura," an import- 

 ant paper by Pro- 

 fessor J. Brun, of 

 Geneva, has just 

 been published in 

 the Proceedings of 

 the Belgian Micro- 

 scopical Society. 

 We have great 

 pleasure in laying 

 the following 

 translation (by Mr. 

 W. B. Hardy) 

 before our 

 readers : — 



Diatoms ; their 

 place in Nature. — 

 Diatoms are all 

 microscopic and belong to the vegetable world. 

 When first they were studied, they were thought 

 to belong to the animal kingdom. Ehrenberg, in 

 consequence of the curious movement with which 

 they are endowed, classed them in 1842 amongst the 

 Infusoria. But numerous investigations made since, 

 by means of the spectroscope and polarised light, have 

 made evident their affinities with certain filamentous 

 Alga?, the Hyalotheca, Zygonema, Spirogyra, &c. Their 

 endochrome, their respiration, and their mode of 

 reproduction, place them without doubt, in the great 

 family of the Alga?, where they form a separate and 

 well-defined class. 



Their abundance. — Diatoms are indeed amongst 

 the most singular objects of the vegetable kingdom. 

 The more one studies them, the more one is 

 astonished to see with what abundance they are 

 distributed in nature : we meet with them nearly 

 everywhere where water is to be found, whether 

 stagnant or running, limpid , or troubled, hot 

 or icy cold, even among the melting snow of the 

 lofty Alps. Everywhere in the deposits of these 

 waters, the eye, aided by the microscope, discovers 

 diatoms, and nearly always in immense numbers. 

 No. 191. 



Their invisible germs are so light (I do not call 

 them spores) that they remain suspended in the air, 

 thus passing from one region to another. Amongst 

 the Alps, these germs are able to remain months 

 without perishing, on the dry rocks exposed to the 

 sun, or on the glaciers exposed to the bitterest cold ; 

 and when a ray of sun comes, and some drops of 

 water, we see them appear by millions ! 



Their dissemination on the Surface of the Globe. — It 

 is by the joint action of the air and water that 

 diatoms are disseminated, and it is the winds and 

 the rains which render their distribution constant. 

 Once dried, their excessive tenuity permits the 

 slightest eddy to sweep them up and spread them 

 abroad over immense tracts of country, and even 

 from one continent to another. When the air 

 becomes calm they gradually settle down. The 

 rains strew this organic dust everywhere on the 

 surface of the soil, and even as far as the highest 

 summits of the Alps, carrying it into the brooks, the 

 marshes, the peat-bogs, and the lakes, and there, in 

 every season, the diatomic dust soon commences to 

 live. This diffusion distributes every species of fresh- 

 water Diatomacea? all over the surface of the globe. 

 Thus we have in Switzerland nearly all the species 

 which have been found in Saxony, by Rabenhorst ; 

 in the environs of Paris, by P. Petit ; in the south by 

 M. Guinard ; in Austria, by M. Griinow, and in the 

 high Tatra of the Carpathians by Schuhmann. 



Nevertheless some species require special con- 

 ditions. Some require salt water, or water contain- 

 ing lime or silica ; others require water perfectly 

 stagnant and warm ; others again prefer water run- 

 ning and fresh ; whilst a few live parasitically on 

 certain species of aquatic plants. Hence, although 

 the same country receives the germs of every species, 

 they do not equally all develope ; it is this which 

 causes the Alps, with their varied conditions of 

 altitude, of heat, of pressure, and of humidity, to 

 support relatively many species. I have collected 

 during eight years six hundred and eighty different 

 species and varieties, and I do not pretend to have 

 found them all, although I have been much aided by 

 my friends of the Alpine Club. Among these species 

 six are new. There are altogether in the known 



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