282 DISEASES OF VEGETABLES. 



it would appear that the defect exists in the eye before 

 its sprouting, because how else can we account for one 

 eye only (the one nearest the umbilical cord) being 

 generally, if any at all are, curled, and no other. 

 Whether it be an insect or a disease we have still to 

 learn. 



In all these cases we find the cellular organisation 

 imperfect and decomposed, and soon afterwards the 

 resort of insects or the seat of fungi. There can be 

 no doubt but that canker is sometimes caused by the 

 attack of insects, by injudicious pruning, or by acci- 

 dental wounds ; but it is equally certain that it appears 

 spontaneously, as if generated by some deleterious 

 quality received either from the soil or situation. 



It is more than probable that canker is transfer- 

 able from one tree to another by intergrafting; we 

 very often see maiden plants attacked by it before 

 they are removed from the nursery ; and though this 

 is generally attributed to the presence of an insect, 

 it is as likely to have been introduced on the graft. 



There is a fungus known among naturalists called 

 ^Ecidium laceratum, which fixes itself on the bark 

 of the whitethorn and pear trees, occasioning canker- 

 ous spots, and consequently pernicious to the plants. 

 It is, however, endemial, and often mistaken for 

 canker. 



Mildew infests many kinds of plants and assumes 

 many different appearances. On peach and nectarine 

 trees, it seizes the tender points of the shoots, which 

 it quickly destroys. On the leaves of the apricot, 



