i6o 



Insefts and Diseases. 



to blight, but results vary so exceedingly, that nearly all efforts have 

 proved fruitless. But among those which have escaped in the 

 largest number of instances may be named, first, the Seckel, which 

 is scarcely ever destroyed even at Cincinnati, and the White Doy- 

 enne. The Madeleine, Winkfield, and Passe Colmar appear to be 

 more liable than the majority of sorts. 



The Blight in the apple and quince, which sometimes kills the 

 terminal shoots on the branches, has been variously ascribed to the 

 sting of an insect and to the effects of weather. The cause does 

 not appear to have been satisfactorily ascertained. It rarely proves 

 a formidable disaster ; but sometimes the trees are much disfigured 

 by it, and temporarily checked in growth. 



The black excrescences on the shoots and limbs of the plum 

 and Morello cherries, Fig. 191, known as the black knot, are pro- 

 duced by the spores of an internal fungus, but sup- 

 posed by some the work of an insect, or the result of 

 diseased sap or cells, or regarded as a sort of vege- 

 table ulcer. They have been by some attributed to 

 the curculio, an opinion originating from the occasion- 

 al detection of this insect within the pulpy excres- 

 cences, but entirely disproved by the facts that the 

 curculio has existed in vast numbers in neighborhoods 

 where the excrescences are unknown ; and on the 

 other hand, that the excrescences have ruined trees in 

 places not infested with the curculio ; besides which, 

 the most rigid search of newly forming knots has 

 failed to detect the eggs or larvae of the curculio, which 

 are only occasionally found when deposited at a later stage in the 

 large pulpy swellings. 



Sufficient evidence appears to have been furnished to prove that 

 a tree, badly diseased, is infected throughout with the poison ; as 

 suckers from such a tree will always sooner or later become affected. 

 Buds from diseased trees, placed in healthy stocks, soon exhibit 

 the excrescences. But seedlings or suckers from a healthy tree 

 usually escape, unless in near proximity to unhealthy trees. 



The remedy for this disease is certain and efficient, if vigilantly 

 applied. It consists in cutting off and burning all the excrescences 

 as soon after their first appearance as practicable. If the tumors, 

 however, break out on the trunk or main limbs, it may be difficult 

 to do this without cutting away the whole tree. As much of the 

 wood is therefore to be cut out as may exhibit indication of disease ; 

 and the wound washed with a solution of chloride of lime. The 



Fig. 191. 



