Mrte Diatomaceae 



H. C WHEELER 



To how many readers does the word 

 "Diatoms" convey any meaning? I 

 think it is safe to assert that for every 

 person who is familiar with these aquatic 

 plants, there are thousands, perhaps 

 more, who have never heard of them, yet 

 everyone who drinks water (a beverage 

 destined to become more commonly 

 used) has very likely swallowed many. 



The diatoms make up an order of Al- 

 gae called Diatomaceae and inhabit both 

 marine and fresh waters. They are re- 

 markable for the formation of a sili- 

 ceous skeleton, which is often beautifully 

 sculptured. So small are the individuals 

 that they appear to the naked eye as so 

 much dust. The tiny A c hnanthes ex- 

 igua, frequent in aquaria, measures but 

 about 12 microns long, while a large 

 species, such as Pinnidaria nobilis, may 

 reach 350 microns. A micron, the unit 

 of measurement, is a thousandth of a 

 millimetre. 



On the death of the organism, the 

 siliceous frame is not readily decom- 

 posed, but sinks to the bottom of the 

 body of water in which it lived. In the 

 course of eons of time sufficient are 

 gathered together to form what is known 

 to the geologists as deposits of "diato- 

 maceous earth." When one contemplates 

 the minuteness of the individual diatom, 

 it seems difficult to realize that some of 

 the deposits in various parts of the 

 United States are hundreds of feet thick. 

 The area occupied by the City of Rich- 

 mond, Virginia, consists almost entirely 

 of such a deposit ranging up to seventy- 

 five feet or more thick. Vast deposits 



occur in California, in Canada, England, 

 Germany, Hungary, Russia and in fact 

 in every country in the world. 



What is their function? When living 

 they assist in purifying the water by 

 liberating oxygen, further, they form an 

 important item in the food of fishes, 

 oysters and other forms of aquatic life. 

 After death their flinty coating is used 

 for such diverse purposes as the manu- 

 facture of tooth powder, metal polish, 

 boiler coverings and dynamite. 



To the student of natural history they 

 furnish a very inviting field and the 

 beauty of their design makes the subject 

 doubly interesting. It was largely due 

 to the efforts of the microscopists of the 

 last century to see their fine structure 

 that the optical perfection of the micro- 

 scope was attained, so it may be safely 

 said that the humble, microscopic diatom 

 has contributed its share to the progress 

 of the world. They are exceedingly com- 

 mon and a student need never be with- 

 out an ample supply of subjects on which 

 to work. I have found upwards of 

 thirty species in our drinking water sup- 

 ply by merely attaching a cheap filter to 

 the faucet in the kitchen. 



Owing to their very small size, and 

 their transparency, the production of 

 photographs suitable for purposes of il- 

 lustration is not always easy. It may be 

 possible, however, to make illustrations 

 of a few of these interesting forms at a 

 future date, and also give concise direc- 

 tions for collecting and preparing them 

 for stuoy. 



