1889. J BOTA NICAL GAZETTE. I I 7 



whole matter. I, That S. diplodictya is not distinct from S, 



crassijulis ; 2, that S. crassijulis is synonymous with S. arc- 

 tica Pall, (which is the main point) ; and finally, 3, the famil- 

 iar assertion that the S. arctica of Pallas is not the S. arctic a 

 of Robert Brown — a statement which can not be made too 

 emphatic, in view of the placid acquiescence, for years past, 

 in the dictum of Andersson to the contrarv. 



It is to regretted that a name grown so familiar as that of 

 S. arctica R. Br. must needs be disturbed ; on the other 

 hand, the open fact of the -priority of S. arctica Pall, can 

 not be ignored \ and as what Sir William J. Hooker was wont 

 to call " Mr. Brown's S. arctica ? ' was only sustained by the 

 constant mention of the name of the distinguished author, let 

 us hope that the substitution of this name for the one pre- 

 occupied may in a large measure preserve unbroken the old 

 associations. 



Rockford, III. 



The Diatom marshes and Diatom beds of the Yellowstone Na- 

 tional Park. 



WALTER IT. \VP;ED. 



It is well known that the minute alg<e, to which the name 

 ot diatoms has been given, possess, in a remarkable degree, 

 the power of separating silica from solution in the waters in 

 which they live. This action is the more remarkable be- 

 cause the silica is often present in such exceedingly small 

 amounts that an almost inconceivable activity on the part of 

 the plant is required to obtain an adequate supply to form 

 their frustules, while the separation of the silica must itself 

 be referred to some vital force exerted by the plant during^ 

 *ts growth. It is this action which gives* to this low form of 

 We its importance as a geological agent. 



As the Diatomacea* exist under very diverse and extreme 

 conditions of environment, occurring' in the icy waters of 

 Polar seas, the heated currents of the tropics, and even in the 

 almost boiling waters of hot springs, they are in consequence 

 the most widely distributed form of life known, and theii 

 common occurrence in ponds and ditches is well known to 

 every microscooist. Nevertheless, contemporaneous deposits 

 t( >mied of theirVemains are usually small in comparison with 



