204 ON THE PERONOSPORiE. 



We now have to examine the next important member of the 

 genus — the Peronospora infestans — or Potato fungus proper, there 

 being really more than half a dozen fungi which affect the Potato ; 

 but none of them equal to this one in importance. The Potato 

 fungus was not included in the collections of De Candolle or 

 Sowerby. The first pubHshed description of the fungus was by 

 Dr. Montague, which appeared in IJ Institute for September, 1845. 

 In November of the same year Payen published an account in A?ift. 

 Soc. Hort. de Paris, and Berkeley's article appeared in t\\Q.Journ. 

 Hort. Society. In December of the same year, Morren published 

 an account of the fungus in the A?in. d^ Agriculture, To Berkeley, 

 then, in this country at least, belongs the honour of having first 

 assigned a fungoid origin to the Potato disease, and still more 

 honour is due to him for having held to the opinion when others 

 wavered. AVe find him writing regarding the fungoid origin of the 

 Potato disease in the Gardejier's Chronicle for 1846, as follows : — 

 *'We come now to the theory which has been so much canvassed, 

 and which is now peculiar almost to Dr. Warren. Of this opinion, 

 notwithstanding the opposition, and in some instances the ridicule, 

 almost, with which it has been assailed, I must profess myself at 

 present." He goes on to say that the decay is the consequence 

 of the presence of the mould, which feeds upon the juices, and 

 prevents the elaboration of nutritive sap in the leaves. 



The first onset of the disease in this country was alarming 

 enough. Appearing first in the Isle of Wight in the autumn of 

 1845, ^t rapidly spread through the South of England. Early in 

 September it appeared in Ireland, and shortly afterwards in 

 Scotland. 



Berkeley's still classical description may be read in the Joiirn. 

 Hort. Soc, or in a more accessible book — " Cooke's Microscopic 

 Fungi." Berkeley clearly established that the disease was due to 

 a fungus, which penetrated by means of its fine mycelium the 

 tissues of the plant, eventually reaching the tubers and involving 

 the whole in a common destruction. It protruded branches 

 through the stomata, which bore two kinds of spores, one of 

 which set free a number of locomotive bodies, capable of pro- 

 pelling themselves through the water by whip-lash-like filaments. 

 Berkeley observed these bodies, but did not detect their cilia, 



