235 



worthless. Even in those drills which had been carefullv moulded, I 

 have seen thai the tubers which grew so near the surface as to crack or 

 break the soil, were damaged by the rot in those places where rain had 

 touched them, whiit-t the tubers which had not been touched by rain, 

 remained free from disease. I have observed that potatoes which grew 

 under the shade or drip of trees, suffered more than those which grew 

 in the open air, and this difierence was so strikingly apparent, that it was 

 evident some deleterious acid had fallen on the potatoes, from the leaves 

 of the trees. 



Sometimes the tips of the leaves are withered by blight ; now it is 

 well known that plants have the power of attracting moisture from the 

 atmosphere, and when the leaves are closed up at night, the tips of the 

 leaves are the first to receive those particles of dew or rain which con- 

 tain the elements of blight. 



Now I think I have proved that the potato rot is caused by nitric 

 acid, which in a highly excited state of the atmosphere, is produced by 

 electricity. That this acid, being condenced by the cold, is attracted by 

 the dew, moisture or rain, and lodges on the leaves of the potato plant. 

 The first part attacked is generally the tip of the leaf; the second, the 

 backs of the leaves; after this the stem, and then the base of the stem 

 immediately adjoining the old seed. 



Some persons who had not sufficiently examined this matter, were 

 led to suppose that the rot commenced in the o'd seed. The reason of 

 this mistake is, that when dew contains but a small portion of nitric acid, 

 it is not strong enough to burn the leaves and stems; but when large 

 quantities of dew are collected by the leaves and poured down at the 

 base of the stem, on the way to the roots, the acid is powerful enough 

 to damage the stem in that place, where it joins the old seed. 



Sometimes the potatoes decome damaged and spotted after they have 

 been taken out of the ground ; tbis is caused by the acid having been 

 absorbed by the roots, and taken into the circulation of the potato, be- 

 fore the tubers become ripe. One of the principal means for prevent- 

 ing the rot, is to have the crop ripe early, and thus out of danger when 

 the season of blight arrives. The next important point in potato cul- 

 ture, is to have the drills so formed, that they shall throw ofl' the rain 

 which at certain seasons contains ingredients hurtful to the tubers. 



Boussingault, the eminent French chemist and agriculturist, states 



