ON A FORM OF SCAB IN POTATOES. 37 



and due exposure to light, air, heat, &c., it follows, that any 

 infringement upon these necessary conditions or laws of nature 

 will tend to render growth unproductive of bloom, by expending 

 the vital forces in the production of abortive shoots. 



IX. — On a form of Scab in Potatoes. By the Rev. M. J. 

 Berkeley, M.A., F.L.S. 



There are two very different diseases known commonly under 

 the name of scab, of which one is far more g'eneral than the 

 other, but, at the same time, less injurious to the intrinsic value 

 of the tubers, though, in point of fact, reducing their market 

 value in consequence of the rough pocky aspect which it pro- 

 duces. 



The first, of which it is not now my intention to treat, was 

 described and figured by Martins (DieKartoffel-Epidemie, p. 23, 

 tab. 2, figs. 9-13; tab. 3, figs. 36-38), and is characterized by 

 the presence of an olive-green or brownisli pulverulent Hy- 

 phomycete (Tuburcinia Scabies, Berk., Journ. Hort. Soc. Lond., 

 vol. i. p. 33, tab. 4, figs. 30, 31), which gives a very peculiar 

 appearance to the pustules, and to which indeed it is not eon- 

 fined, but occasionally forms a stratum a line or more in thick- 

 ness beneath the greater portion of the cuticle. A few scattered 

 tubers occur now and then affected by this disease, but it is very 

 rarely so prevalent as to draw much attention. The potato-crops, 

 how-ever, suffered greatly from its ravages in the Scilly Islands 

 and in Cornwall during the present summer, where it appeared 

 under a very destructive form. Mature specimens were for- 

 warded to me, with the promise at some future period of a 

 supply of tubers in every stage of the disease. I was, however, 

 disappointed in my hope of being enabled to investigate its 

 nature more closely, possibly because the malady, as Martins 

 reports, is several weeks in going through its phases. Indeed, 

 it should seem that, in Germany, it does not usually occur till 

 after the tubers have been raised for pitting ; and as it first appears 

 under the form of discoloured spots, which gradually spread and 

 become confluent, and of which the cuticle is not at all ruptured 

 for some weeks, it has been supposed by the German peasants to 

 arise from injuries received by the tubers in the course of har- 

 vesting. Tins notion seems, however, to be completely contra- 

 dicted by the fact of its occurring to a considerable extent on the 

 tubers in situ. 



The second disease which passes, though perfectly distinct, 

 under the name of scab is extremely common in newly turned 

 up soil, especially if it contain cinder-dust or lime rubbish, or 



