On the Potato Disease. 73 



an increased transpiration was necessary, but was always checked 

 by the increased pressure of vapor in the middle of the day ; this 

 of course deranged the circulation and caused the liquids in the 

 circulation to begin to ferment. This view is supported by the 

 fact that in Holland the parts first attacked were the leaves and 

 stalks, the parts more directly in contact with the air. In Scot- 

 land and some parts of Prussia the disease made its appearance ill 

 September, for the most part ; the temperature of the earth was 

 then higher than that of the air, and accordingly the disease gen- 

 erally attacked the tubers first. But when we acknowledge all 

 of these extraordinary facts, we still are forced to look for some 

 special predisposition to disease among the potatoes themselves. 

 In what this special predisposition consists, it is not easy to say. 



It has not been the same in all species of potatoes, some have 

 almost escaped while others of another kind in the same neigh- 

 borhood have been almost utterly destroyed ; it must reside in 

 the plant itself, either in the structure of its tissues, or in the 

 chemical state of its juices. It has been noticed that the potatoes 

 of late years have had a much greater tendency than usual to 

 germinate. This indicates an unusual molecular movement in 

 the juices, which under the influence of moisture and the atmo- 

 sphere, in place of changing the starch into dextrine and dextrine 

 into cellulose, ferments and causes the disease. 



Potatoes planted during the early morning have in some in- 

 stances been almost entirely free from the malady, while those of 

 the same variety planted in the afternoon, after lying in the sun 

 sometime, were almost all destroyed. In this case, it seems possi- 

 ble that the heat of the sun gave a movement to the juices and 

 prepared the way for the subsequent attack. 



Von Martius describes two distinct kinds of disease, De Drooge 

 kankerachtige Ziekte der Aardappelen, the dry canker disease of 

 Jhe potatoe, Gangrsena tuberum Solani ; and " De schurftachtige 

 Ziekte der Aardappelen," the scabby disease of the potatoe, Por- 

 r *go tuberum Solani. 



am 



ground for very probable theories as to the cause of this dis- 

 use, and indicate the course to be taken in future investigation. 

 l h as seems possible, atmospheric influences induce such chemi- 

 " ol -*" * growing crops, though we have found a cause, 



cal 



w e have not found a remedy ; to guard field crops from atmosphe- 

 re changes is not an easy matter. 



Such changes may occur only at long intervals of years, but 

 th e fact of their occurring at all, will be a warning to the nations 

 ?°t to place their sole dependence on a single crop. Unhappy 

 Ireland and the north of Scotland are mournful examples of 

 tn 's mistake 



Utrecht, April 25, 1847. 



Secosd Series, Vol. IV, No. 10—JuIy, 1847. 10 



J. P. N. 



