992 :\rALFORMATio>:s and diseases 



Hist. Nat. iv. p. 115. ; Palletta, in Atti della soc. patriot, di 

 Milano, Re. p. 303. 



The canker proceeds mostly from a hardening of the bark, 

 in consequence of wliicli the juices become sharp and corro- 

 sive, make tlieir way through the rents and slits of the rind, 

 consume the parts that are below them, and at last complete- 

 ly destroy the wood. 



422. 



Our Corn crops are injured chiefly by parasitic plants of 

 the lowest class. The rust upon the leaves and stalks is no- 

 thing but a Puccmia, which closes up the epidermis of the 

 leaves, and thereby destroys their functions. Whether this 

 plant is generated by the jEcid'mm Berberides^ is a matter of 

 much uncertainty ; (Sir Jos. Banks on the Blight in Corn, 

 in Ann. of Botany, ii. p. 51.) 



The flying blight, by which Oats and Maize are chiefly in- 

 jured, consists, as we formerly remarked, of an innumerable 

 multitude of spherical black Coniomyci (Ustilago segetum), 

 which presuppose a degeneration of the grain, and by which 

 it is completely consumed. The soiling blight (Uredo sito-- 

 phila, Ditmar.), on the other hand, contains smaller grains 

 within a spherical covering, and is instantly discovered by 

 its disagreeable smell, resembling herring-pickle. ^Vhat more 

 remote causes, beside the formerly mentioned predisposition of 

 the grain of AVheat, contribute to the production of this evil, 

 is not quite clear. But the infectious nature of this species 

 of Coniomyci cannot be denied. So strong, indeed, is this 

 tendency, that it clings to the glumes or caps of the wheat 

 grain, and even to the iine hairy bodies Vvhich rise upon 

 the jx)ints of the grain. The steeping of the grain in lime, 

 and in a solution of common salt, cleans the Wheat indeed in 

 most instances from any adhering rust ; but the manure itself, 

 if it be mingled with wheat-straw that had been blighted, 

 communicates to the wheat, which is grown upon lands so ma- 

 nured, the diseased tjuality. It is not impossible, that even the 

 want of a free circulation of air in v/heat fields, or the too 



