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evident about it; that it is not a local disease. 

 For even if you cut off the diseased portion 

 of the plant itself, the disease continues. And 

 if you cut off the diseased portion of the po- 

 tato root or tuber, the disease continues in the 

 rest of it. It is, therefore, probable that it is 

 a disease of the sap and cellular tissue, and 

 thus affects the vital action of the whole plant. 

 This idea derives probability from the fact 

 that the common potato has been for years so 

 cultivated as to produce an undue proportion 

 of these constituents of the plant. And Dr. 

 Smee reports, that the wild J otatoes growing 

 in the horticultural gardens at London are but 

 little affected by this disease. Though they, 

 too, have it, it produces no serious injury to 

 their roots. 



Among the alleged causes of this disease, 

 (and their name is legion,) is cold. Every 

 plant requires a certain temperature in which 

 to exist, and alterations of it will certainly 

 produce its destruction. But during the last 

 three years there has been no such alteration. 

 The last year has been rather remarkable for 

 the unwonted mildness of its winter and heat 

 of its summer, both in this country and in 

 Europe. This cannot, therefore, be its cause; 

 nor would it have been a probable supposition, 

 even if there had been any such change of 

 temperature, as the potato is a plant which 

 flourishes under as wide a distribution of tem- 

 perature as any whatever. 



Light has been assumed to be the cause of 

 the disease. Every plant requires a certain 

 degree of light to exist and some are killed by 

 too much of it. A correspondent in a late 

 number of this paper supposes that the disease 

 has been caused by keeping our seed potatoes 

 above ground, after they are dug, instead of 

 burying them. We think this £ very impro- 

 bable cause, because it is known that exposure 

 to light renders the potato exceedingly fit for 

 planting, and seems to increase their vitality. 

 It renders them prone to sprout. But even if 

 this could produce the disease, it has never 

 had much opportunity for affecting the tuber; 

 as after digging they are. usually kept in cel- 

 lars and store houses, places in which they 

 are little exposed to the action of light. 



Electricity has been supposed to be capable 



of producing the rot; but we have no reason 

 to suppose this element has existed in an un- 

 due proportion during the last few years, nor 

 that the potato has been more exposed to it 

 than it always has been. In the same way 

 moisture has been assumed to be the possible 

 cause, and various winds; but these theories 

 have as little support. Various kinds of soil 

 have been declared to be the cause. But the 

 disease has long since attacked the plant on 

 every variety of soil. Manures have next 

 been discussed, and every kind has been 

 blamed, guano, especially. But it also attacks 

 potatoes with and without manure. They 

 may do harm, however, in causing the plant 

 to assume a very succulent and cellular cha- 

 racter. 



A great number of fungi, or vegetable para- 

 sites, have been observed upon the diseased 

 potatoes, and these were long thought to be 

 the cause of it. But these fungi have never 

 been observed upon the potato until the disease 

 has not merely begun, but progressed to an 

 advanced stage. In truth, fungi upon diseased 

 plants of every kind are a wise provision of 

 nature to carry off decayed matter. They 

 are never the predecessors, but they are very 

 generally the followers of disease in plants. 

 They perform the same office in the vegetable 

 kingdom that the carrion crow, the beetle, &c. 

 perform in the animal kingdom. Nature when 

 left to herself, always provides for the removal 

 of dead material, and her usual method is to 

 convert death into life. To the fungi are left 

 the duty of annihilating the exhalations of de- 

 caying vegetable matter. No sooner does a 

 portion of a plant become diseased than the 

 fungi grow thereupon, removing the soft de- 

 caying parts, and thus converting dead into 

 living matter. A far more plausible theory, 

 is that the plant has been for years propagated 

 in an abnormal manner by cuttings instead of 

 by seed, and that its vitality has been thereby 

 worn out. If this be the true cause of the 

 disease, all that is to be done to cure it, is to 

 rear the potato from the seed again. There 

 are many circumstances tending to substan- 

 tiate this theory. There has been evidently 

 a great loss of vitality in the potato during 

 late years. It has very generally ceased ta 



