24 Diseases of the Potatoe. 



Mr. John Shirreff takes a general and philosophical view 

 of the cause of disease in the potatoe crop, and though, no 

 doubt, his observations are particularly applicable to the curl, 

 still they will apply equally well to the taint ; for the con- 

 nection between the two diseases is so intimate, that you have 

 seen Mr. Dickson's observation is, that some sets " did not 

 vegetate at all," that is, failed, " or produced curled plants." 

 Mr. Shirreff adopts the general doctrine broached by Mr. 

 Knight. " The maximum of the duration of the life of any 

 individual vegetable or animal," he says, " is predetermined 

 by nature, under whatever circumstances the individual may 

 be placed ; the minimum, on the other hand, is determined 

 by these very circumstances. Admitting, then, that a pota- 

 toe might reproduce itself from tubers for a great number of 

 years in the shady woods of Peru, it seems destined to be- 

 come abortive in the cultivated champaign of Britain, inso- 

 much that not a single healthy plant of any sort of potatoe 

 that yields berries, and which was in culture 'twenty years 

 ago, can now be produced." Mr. Shirreff concludes, there- 

 fore, that the potatoe is to be considered a short-lived plant, 

 and that though its health and vigor may be prolonged by 

 rearing it in elevated or in shady situations, or by cropping 

 the flowers, and thus preventing the plants from exhausting 

 themselves, the only syre way to obtain vigorous plants, and 

 to ensure productive crops, is to have frequent recourse to 

 new varieties from seed. The same view had occurred to Dr. 

 Hunter, who, in his Georgical egsays, has limited the duration 

 of a variety in a state of perfection to fourteen years. 



The fact ascertained by Mr. Knight deserves to be noticed. 

 That by planting late in the season, an exhausted good 

 variety, may, in a great measure be restored ; that is, the 

 tuber resulting from the late planting, when again planted at 

 the ordinary season, produces the kind in its pristine vigor 

 and of its former size. It is obvious that all these opinions 



