CH. VIII.] THE DISEASES OF PLANTS. 255 



to enable me to attempt a classification of their dis- 

 eases. Neither shall I attempt in this volume to 

 enter upon the consideration of the injuiies to which 

 plants are subjected either from predatoiy insects, or 

 from parasitical plants : my space will not permit 

 this, and I regret it the less because they ai'e now 

 the subjects dwelt upon by master minds in the 

 pages of the Gardeners Chronicle. 



The Curl. — Xo disease appears to me to arise 

 from impau'ed vital energy in the plant more 

 clearly than the curl, that of late years has made 

 such extensive ravages upon our potato crops ^. Any 

 one can insure the occurrence of this disease, at 

 least I have found it so in the county of Essex, by 

 keeping the sets in a situation favourable to their 

 vegetation, as in a warm damp out-house, and then 

 nibbing off repeatedly the long shoots they have 

 thrown out. Sets that have been so treated, I have 

 invariably found produce curled plants. Is not the 

 reason very apparent. The vital energy had been 

 weakened by the repeated efforts to vegetate; so 

 that, when planted in the soil, their energy was 

 unequal to the perfect developement of the parts ; 

 for the curl is nothing more nor less than a distorted 



* The opinions of Mr. Monro, of Brechin Nursery, coincides 

 with mine. He considers " weakness is the cause " of the dis- 

 ease. — Gardeners Magazine, xi. 417. 



