72 On the Potato Disease. 
entirely. The brown and black parts contain a greatly increased 
proportion of insoluble matter; the increase is chiefly owing to 
the deposition of brownish granular matter, in the cells. This 
matter is insoluble in water, in ether, in boiling alcohol, im acids 
or alkalies, and exhibits most of the properties of ulmin, result- 
ing from the composition of the substance contained in the cellu- 
lar liquids. e will here quote Prof. Harting’s words. 
‘Cette matiére est le resultat des transmutations qu’ont subies 
Valbumine et la dextrine dissoutes dans le suc cellulaire, et de la 
fécule, que, apres s’étre transformée en dextrine, y contribue aussi. 
“Tl est trés-vraisemblable que c’est l’albumine, qui soit transfor- 
mée la premiére, puis la dextrine, enfin la fécule, qui résiste le 
plus long-temps, et dont l’alteration est encore peu visible méme 
aun état trés-avancé de la maladie. 
“'Tontes ces transformations chimiques, appartiennent a cette 
grande série de phénoménes, comprise sous le nom général de 
fermentation, et qu’on pourrait désigner ici plus particuliérement 
par le nom @’humification, or d’ulmification.” 
He thinks that we may observe the same things every year in 
apples, pears, &c. The same granular brown matter is shown 
the microscope in the cells, and by chemical analysis is proved to 
be idéntical with the brown matter of the potatoes. 
Prof. Harting, led on by these facts, sought to find in the tem- 
perature of the air and earth, the cause of this disease. He has 
collected a large number of observations upon this point. ‘The 
winter of 1844-1845 was long and rigorous, and the cold espe- 
cially severe during March. The equilibrium between the air 
and the surface of the earth, when a change took place, was thus 
disturbed, the earth becoming warm much more slowly than the 
air. The early planted potatoes then found the ground in an 
unfavorable state. The year 1845 is compared with the prece- 
ding years as far back as 1838. The month of March was ex- 
cessively cold as noticed above, the month of April was a little 
warmer than the mean of the preceding Aprils; May was very 
rainy, and the temperature below the minimum of preceding 
years. June, on the contrary, was very hot, above the former 
maximum, July was also very warm with much rain, so that the 
potatoes grew with much rapidity. The variations of the ba- 
rometer were not greater than ordinary, but the case was far 
otherwise as to the humidity of the air and the pressure of vapor. 
During the months of July and August, the relative humidity 
was above the maximum of the same months in preceding years} 
in those years also the pressure of vapor was less at two in the 
afternoon than at eight in the morning, but in 1845 this rule was 
rev: he malady in Holland ended in the month of July, 
and after the middle of that month the above differences were 
not more perceptible. The great heat of the air and excessive 
moisture caused a rapid developement of the plant, and of course 
