340 Potato Disease. [Dec, 



Potato Disease. — Mr. C. R. Bree said: In September, 1846, 

 I ventured to suggest that we should endeavor to arrive at 

 sound conclusions about the nature and cause of the potatoe dis- 

 ease, by registering and reasoning upon facts alone. I also stated 

 that for two years I had observed symptoms of the disease for the 

 first time on the 23d of August. When I observed, therefore, 

 your notice of the 20th ult., that we had nearly escaped the dis- 

 ease, I could not help thinking that the remark might still be 

 premature, and the experience of the last 10 days (1 wi'ite Sept.. 

 1,) has unfortunately verified — at least partly — the truth of my 

 anticipation. Previous to the heavy rain which fell throughout 

 this district in the thunder-storm of the 16th of August, I heard 

 no complaint of disease; I had not a vestige of it in my own gar- 

 den, nor could I hear of it in those of my neighbors, with one 

 exception, and that of a limited character. Between the 16th 

 and 20th of August rumors q^ disease in this neighborhood sprung 

 up, and by the 30th it became general. In some instances the 

 loss is as great as in 1845. We thus find that in the three yeais 

 this pestilence has destroyed our potato crop, it has invariable ex- 

 hibited itself most severely and extensively between the 15th and 

 31st of August. This fact allowed, we make one step towards 

 a rational description of the disease. Now, with regarding 

 its nature. It appears in different parts of the plant at the same 

 time, in the form of small black patches, resulting from the death 

 of a portion of the tissue of the plant. These blotches in the 

 leaves are generally dry, and crumble beneath the touch, and in 

 some instances (the great majority) are covered with a parasiti- 

 cal fungus, the Botrytis Infestans. No person I think who has had 

 the slightest experience will fall into the great error of attributing 

 the accession of the blotches to the injury caused to the leaf by an 

 aphis or any other insect. The two phenomena are widely dif- 

 ferent. The aphis causes the leaves which it infests to curl and 

 form hollows, in which it generally is found to congregate in 

 large numbers long Ijefore the vitality of the leaf is affected. 

 This is not the case with the potato disease. I have looked care- 

 fully through my rows without finding an aphis of any description; 

 but there is no mistaking the dark, isolated, gangrenous-looking 

 spots, which are appearing on the leaves, along the stems, and 

 among the tubers. How is this? I take up a root, and find five 

 tubers perfectly sound and one diseased. I look at once at the 

 stem and leaves and I find patches of the well known disease iso- 

 lated, perfectly distinct from each other. Now I know of no law 

 in vegetable physiology which enables an insect to cause pheno- 

 mena like lliese. The notion is too absurd; it will not bear a 

 moment's examination. In one of ray deductions last year I sug- 

 gested the soil might have a greater or less influence in effecting 

 a change in the vital process; but 1 find that the gardens on our 



