On the Potato Disease. V3 
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 
citculation 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 in 
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. 
t 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 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 1n- 
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 possl- 
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 
the potatoe, Gangrena tuberum Solani; and “ De schurftachtige 
Ziekte der Aardappelen,” the scabby disease of the potatoe, Por- 
te changes i matter. 
Shines ney SE only at long intervals of years, but 
the fact of their occurring at all, will be a warning 
hot to place their sole dependence on a single crop. Unhappy 
Ireland and the north of Scotland are mournful examples of 
this mistake. PLN: 
Utrecht, April 25, 1847. | 
Srconp Series, Vol. IV, No. 10.—July, 1847. 10 
