118 ON "parhelia millaniana." 



tint " by apj^lying solution of iodine after liq. potassae ; and^ 

 indeed, all my experience tends to prove that these two chemicals, 

 whether applied together or consecutively, only nullify each other. 

 May I be permitted to hint the possibility that Dr. Stirton has had 

 under his microscope a section of an apothecium of some other 

 lichen which has accidentally grown strayingly on the same piece 

 of wood with the Arthonia ? I shall have great pleasure in send- 

 ing Dr. Stirton a specimen of true A. lurida, if he will signify his 

 wish thereanent, W. A. Leighton. 



NATUKAL HISTORY OF DIATOMACE.E. 



£^ Dr. a. M. Edwards. 



Dr. Edwards has sent us a copy of the chapter from the Reports 

 of the Geological Survey on the above subject, which is written in 

 a popular style for general readers, and extends over nearly 100 

 quarto pages. The sections into which it is divided are 1. Intro- 

 duction ; 2, Movements of the Diatomacese. 3, Mode of growth 

 of the Diatomaceje. 4, Reproduction of the Diatomacese. 5, 

 Modes of occurrence and uses to man of the Diatomaceee. 6, 

 The Diatomacege and Geology. 7, Directions for collecting, pre- 

 serving, and transporting specimens of diatomacese. 8, How to 

 prepare specimens of diatomacese for examination and study by 

 means of the microscope. This enumeration of the sections will 

 give an idea of the scope of the "History," which will doubtless be 

 of eminent service in the direction for which it is intended. Un- 

 fortunately the general public know but little, and care less, about 

 the lower Cryptogamia, except for Algje grouped as pretty objects 

 for the drawing room, or ornate diatoms arranged in groups to 

 please soiree hunters, or stewed mushrooms, and Perigord pies. 



Onion Blight in the United States. — "We have received 



the Annual Report of the Department of Agriculture for 1872, 



and find an account (at p. 193) of a destructive onion blight 



which had made its appearance in a field of growing onions. The 



cause is supposed to be a sj^ecies of Peronospora, but the rough 



figures forbid any such conclusion. It is very much more like a 



species of Fusispovium. There would appear from the description 



to be at least three parasites, one of which is an Oidiiim, and the 



other (beside the Fusisjiorium ?) it is very difficult, as the writer is 



1 evidently no mycologist, to make out from either the rude figure or 



J J. I the vague description. The spores as figured resemble those of 



' Urocystis ; but if they are produced on the branches of erect 



threads, then they belong to quite another order, and may be some 



black mould [Dematiei). If so, the Fusisporium (?) ox' Oidium are 



much more likely to be the cause of the disease. 



