194 Disease in Plants. 



upon tlie plants of each plot, that the proximate cause of the 

 destructive malady is to be sought for in the soil. Wherever 

 the soil furnishes in sufficient quantity and proper proportions 

 the elements required for the structural development and active 

 working- of the plant, then the plant obtains thereby a power of 

 resisting noxious influences from without sufficient entirely to 

 obviate their bad effects. 



These facts throw the clearest light upon diseases of plants in 

 general — for instance, upon the so-called vine-disease ; and I 

 entertain no doubt whatever that this and the silkworm-disease 

 are explained by a change in the constitution of the soil or 

 by its exhaustion. 



Nowhere, in no single spot, has any one yet succeeded by the 

 employment of any of the usual remedies in guarding against a 

 return of the vine-disease. Even where, in the early years, the 

 grape-fungus was dispelled by one dose of sulphur-powder, a 

 fourfold application now fails to save the crop ; and it can be 

 distinctly foreseen that in course of time the use of sulphur for 

 this pui'pose will become perfectly vain. 



The foundation of the silkworm-disease is simply this, — that 

 the mulberry-leaves no longer contain in proper quantity and 

 form those constituents which are essential to the healthy growth 

 of the worm : in other words, the ground can no longer fulfil 

 the conditions requisite to supply those elements which are 

 necessary for their production, and which, without renewal, have 

 for centuries been withdrawn from it. The worms fed on these 

 leaves die before spinning their cocoons, and in this way the silk- 

 crop in North Italy has continuously diminished for the last 

 sixteen years. 



On travelling in North Italy 1 found that wherever the grape- 

 disease prevailed, there too the mulberry gave no more silk, but 

 where the silkworm was flourishing the vine-plant was sound. 



If the silkworm is fed on leaves taken from trees or shrubs 

 newly planted in places where no similar tree has ever grown, 

 and where the soil is still fully furnished with the food of these 

 plants, it is then quite healthy and produces silk. 



It is difficult adequately to represent the magnitude and extent 

 of both these evils in Northern Italy. For the last ten years no 

 wine has been made ; yet wine is there as important an article of 

 common consumption as beer is in Germany. As a consequence 

 of the lamentable falling off in the supply of silk, the wealth of 

 Lombardy is disappearing and an impoverishment of the country 

 is setting in. Hundreds of families which once were in com- 

 fortable circumstances have been reduced to want. Estates on 

 the Lake of Como, with elegant villas, which formerly com- 

 manded an income of 100,000 fr. (4000/.) can now find no pur- 

 chasers at a fifth part of their former value ; and the industrious 



