48 RELATION OF THE DISEASE TO EXTERNAL CAUSES. 



(182.) The potatoe plant has a wide distribution, and 

 lives under varied circumstances better than most other 

 plants, as I have before observed. . 



(183.) If the life and death of a plant depend upon the 

 variations of temperature, it is fair to suppose that lesser 

 alterations of temperature will influence the health of the 

 plant, and, in some cases, tend to disease. 



(184.) Cold has been assumed as the cause of the 

 present potatoe disease ; but if we look to the average of 

 three years, during which the disease has been known to 

 be prevalent, we find that it cannot be from that cause. In 

 fact, the spring and summer of 1846 have been remarka- 

 ble for their extreme heat, so much so that the out-door 

 grapes have attained extraordinary perfection, and the 

 larger kinds of Indian corn have completely ripened in the 

 open air. 



(185.) Temperature does not cause the disease, although 

 it has an important influence upon it. In the first place, 

 when the disease cuts off the supply of the sap from the 

 leaflet, the leaf and the stalk, or the entire haulm, it fre- 

 quently happens that a very hot day will affect a large plot 

 of potatoe haulms at once, and dry them up. 



(186.) I watched the potatoes the first thing in the morn- 

 ing before I went \o business, the moment I returned, and 

 the last thing at night ; and there were hot days when the 

 change produced from this cause exceeded all belief. 



(187.) Temperature has an important influence upon the 

 decay of the tuber ; and it has so happened that in ships' 

 cargoes, where the potatoes were sound when put on board, 

 yet when they were in the ship's hold they became heated, 

 and not one sound one remained. In fact, I have been 

 informed that many tons were in such a bad state last year 



