27 





PERONOSPOEA INEESTANS. MONT. 



Potato Peeonospoea. 



By E. A. Bastow, E.L.S. 



Bead May 18, 188G. 



Natitbal oedbe VIII. — Fungi. 



SUB-OEDBB IV.— HypHOMYCETES. 



Teibe XVII. — MiiOEDiifEs. Hooker's Handbook. 



Peronospora infestans. Threads of mycelium slender,, 

 always destitute of suckers ; fertile thread thin gradually 

 attenuated upwards, with one to five branches ; branches either 

 simple or with short branchlets ; acrospores ellipsoid or ovoid, 

 apex furnished with a prominent papilla. Coolie's Handbook of 

 British Fungi, p. 593. Cooke Micro. Fungi, t. 14 ; f. 264 ; p. 

 155. Fop. Sc. Review, vol. iii; t. 8 ; f. 3; p. 193. vol. xiii; p. 151. 

 Botrytis infestans, B. and Br. Ann. N. II. No. 521. Journ. 

 Hort. Soc. vol. 1 ; t.4 ; p. 11. De Bary. Ann. Sc. Nat., (1863), 

 xx. t. 5 ; vol. 6. Monthly Mic. Journ., 1874, 1875, 1876. Science 

 Gossip, vols, xii., xiii. Gard. Citron., 1875, 1876. 



On potato stems, leaves, and tubers. 



Many theories have been advanced with regard to the origin 

 of the destructive Peronospora infestans or potato disease. 

 Meteorological and electrical states of the atmosphere, 

 saturation of the plant by water, degeneration by various 

 methods of cultivation, the ravages of insect life, these and 

 others have each in their time been brought forward as the 

 cause of all the mischief with our potato crops. But the last, 

 twenty years of scientific inquiry by Messrs. Cooke, Berkley, 

 De Bary, and more especially the researches of Mr. W. G. 

 Smith, of Mildway Grove, London (to whom was awarded the 

 Eoyal Horticultural Society's Gold Medal for his discoveries),^ 

 has done much towards the completion of the life history of 

 this withering blight, many proofs have been obtained of its 

 fungoid origin, and its growth and method of reproduction has 

 been most assiduously traced in its several forms as far as 

 modern appliances will allow of investigations being made. 



Eor much information concerning P. infestans given in this 

 paper, I am indebted to Mr. W. G. Smith, who, in reply 

 to my numerous queries in 1879 took the greatest pains to 

 make points clear of which I was doubt M, and could not 

 without assistance come to any definite conclusion, and wbo 

 also liberally supplied me with slides for comparison. 



When the potato plant has been attacked by the disease, 

 the leaves assume a pale tint, and discolored spots appear 

 thereon ; if, in this stage of the disease, the underside of the 

 leaf is examined it will be found to be covered with whitish 

 patches, these patches are stems with fruit, and arise from the 



