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, in 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. We will here quote Prof. Harting's words. 



" Cette matiere est le resultat des transmutations qu'ont subies 

 l'albumine et la dextrine dissoutes dans le sue cellulaire, et de la 

 fecule, que, apres s'etre transformed en dextrine, y contribue aussi. 



"II est tres-vraisemblable que e'est Palbumine, qui soit transfor- 

 mee la premiere, puis la dextrine, enfin la fecule, qui resiste le 

 plus long-temps, et dont Palteration est encore peu visible meme 

 a un etat tres-avance de la maladie. 



" Tontes ces transformations chimiques, appartiennent a cette 

 grande serie de phenomenes, comprise sous le nom general de 



fermentation, et qu'on pourrait designer ici plus particulierement 

 par le nom d } hiimification , or flulrnijication" 



He thinks that we may observe the same things every year in 

 apples, pears, &c. The same granular brown matter is shown by 

 the microscope in the cells, and by chemical analysis is proved to 

 be identical 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 fa** 

 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 

 reversed. The 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 



