The Potato Disease. 511 



unknown of the potato fungus has been brought to light ; 

 and its entire life-historv is now as well understood as that 



*j 



of the commonest plant of our tillage. 



In June, 1875, Mr. Worthington G. Smith, of England, 

 an enthusiastic joung artist-botanist, aided bv suggestions 

 received from Rev. M. J. Berkley, the most eminent of 

 British fungologists, discovered the resting-spores, the 

 wintering seeds, of Peronospora irifestans, learned the 

 mode of their production, and, by aid of his camera 

 lucida, clearly sketched the plant in all its parts. 



And, during the past season of 1876, incited thereto by the 

 adverse and somewhat arrogant criticisms of De Bary, 

 vtdth the utmost patience and care, working almost day 

 and night, he has gone over the ground again, and has 

 completely confirmed his previous observations, besides 

 detecting and lucidly sketching several new phases in the 

 life-history of the fungus ; and in this his own observations 

 have been sustained, step by step, by the simultaneous and 

 parallel observations of several other acute English 

 cryptogamists. The resting-spores of the previous year, 

 preserved successfully through the winter, have, in numer- 

 ous cases, been made to germinate and to go through then- 

 entire cycle of growth, as previously observed. 



A study of other species of Peronospora, allied to the 

 one which produces the potato disease, has revealed the 

 fact of a third mode of reproduction. The simple-spores and 

 swarm-spores, already described, are termed asexual, 

 because they are without sex. Not being formed by the 

 union of the two sexual elements of the plant, they are but as 

 buds, shed off by the mother plant, and only endowed 



