660 POTATO ROT. 



"It is in the air," appears often to be thought a satisfactory ex- 

 planation. If we ask for proof, none can be obtained either 

 from chemistry or meteorology. If atmospheric, then the cause 

 of the evil is likely at once to be beyond our cognizance and 

 control ; besides, we are at a loss, on this hypothesis, to 

 account for the apparently almost entire limitation of the dis- 

 ease to one cultivated plant. 



On the contrary, every point in the nature of the disease, and 

 the means hitherto found useful in counteracting it, indicate 

 that the defect is in the plant itself; that from some cause its 

 vital force has been weakened, so that putrefactive processes 

 lay hold on the substances, which in a healthy state it could 

 retain unchanged ; and that these putrefactive changes can be 

 arrested only when the circumstances are in all respects 

 healthy ; while unfavorable circumstances, which in former 

 years produced no eifect, are now speedily fatal. 



Is there, then, anything in the past history or present condi- 

 tion of the plant, likely to produce such an effect? I have 

 long thought that there is such a cause, and shall now proceed 

 to explain it, in connection with the only means of counterac- 

 tion which have suggested themselves. 



Of all our crops, the potato alone has been continuously 

 propagated by natural or artificial division of the plant. The 

 tuber of the potato is a sort of underground stem, with eyes or 

 buds intended to produce young shoots in the year following 

 the formation of the tuber, and with a store of starch, albumen, 

 &c., to nourish these young shoots in the early stages of their 

 growth. These tubers, then, in the natural state of the plant, 

 must serve to continue its existence from year to year, and to 

 extend the individual plant into a group or bed of greater or 

 less extent. But this process is not intended to be perpetual. 

 The longest lived forest tree must eventually die, and so must 

 the group or stool of the potatoes, which, originally founded by 

 a single seed from a ball, is only one plant increased in extent 

 by a spontaneous division of its roots into detached tubers. It 

 gradually exhausts the neighboring soil, and its own vital en- 

 ergy diminishes, and at length it will die out ; and if a new 



