the Cultivation of Potatoes. 229 



it seems gradually to have abated. Various have been the opinions concerning it, 

 but none which carry with them complete conviction. The opinion which I lean 

 to (and I only lean to it) is, that the disease is hereditary ; in the same sense, I 

 mean as certain diseases are said to be hereditary in certain families, which though 

 they do not regularly appear in every generation, yet are always liable to break out 

 on the slightest agency of the exciting cause. One circumstance which tends to 

 favour this opinion is, that some sorts, the ox-noble for instance, were never 

 infected with tliis disease. I have remarked that the sets producing curled plants 

 seldom dissolve, coming up in autumn to all appearance in as perfect state as when 

 first deposited in the ground. 



It has been said, and if I mistake not, I once proved it by experiment, (but as 

 it is many years since, and as I took no memorandum of the fact at the time, I 

 cannot trust to the accuracy of my recollection) that a potatoe, which cuts hard or 

 woody, will infallibly produce curled plants, and such as yield freely to the knife, 

 may be expected to produce healthy ones. 



X. General Observations. 



It is a received maxim that the same crop ought not to be grown on the same 

 land for a succession of years, under the idea, I suppose, that to bring any parti- 

 cular vegetable to maturity requires a specific kind of nutriment, of which in a 

 short time the soil would be exhausted, were it to produce the same species of plant 

 annually. There is reason to believe that this idea is erroneous. I mean not, how- 

 ever, to say that a rotation of crops is not in general beneficial, and in most cases 

 even necessary. 



A rotation of crops enables the farmer to repair the exhaustion of one crop, 

 •which is reaped and carried off the ground, by the interposition of another, which 

 being manured for, and consumed upon the land, brings back as much as the 

 preceding one had taken away. Besides, a rotation of crops, of which turnips and 

 vegetables of that tribe make a part, gives time for eradicating couch-grass and 

 other weeds, which will unavoidably accumulate amongst every kind of grain which 

 admits not of garden culture. Were it practicable to cultivate even wheat, so as that 

 the crop could be produced every year perfectly free from weeds, the same grain 

 might be repeated ad infinitum by the assistance of sufficient manure to make 

 good the annual exhaustion of the soil. 



