533 



known, that large quantities of potatoes, heaped together, always pro- 

 duce a slight heat which, as a matter of course, would be increased 

 by the decaying material of the diseased tubers, to a degree, it is rea- 

 sonable to suppose, that would prove injurious to the whole heap, es- 

 pecially if many of them were effected. Indeed, one instance is 

 recorded by Professor Henslow of spontaneous combustion being 

 nearly generated by a heap of decaying potatoes. When the heaps 

 have been attended to, and occasionally turned over, having the dis- 

 eased tubers picked out, T believe they have kept as well as they 

 usually do, without further trouble. 



It is apparent that much of the success of this year's crop depends 

 on selecting sound seed ; for, although diseased tubers vegetate and 

 produce plants, they are mostly weak, and certainly liable to decay ; 

 and very many of them will fail if used, because it is to be observed, 

 that the conditions necessary for active vegetation are, precisely, those 

 conducive to putrefaction, which may become too powerful for the 

 vital force to resist, before the young shoot has increased sufficiently 

 to be independent of the old tuber for support. 



With reference to the decay which has already manifested itself 

 this season, I am not prepared to offer a decided opinion as to whe- 

 ther it is the result of last year's disease, or a modification of it : but 

 in most of the cases which came under my observation, from 

 plants raised in the Garden, as well as those sent to me from the 

 country, the decay is clearly traceable to the old tuber. It takes 

 place on the lower portion of the stem, generally close to the tuber. 

 In some of the worst cases I could not observe that the Botrytis had 

 been produced on the leaves, but in two instances it was very evident 

 and agreed, in every way, with the specimens collected last season by 

 the Rev. Mr. Berkeley, and kindly communicated to me. In such 

 cases, however, had sound seed been used, it is probable that we 

 should have had no appearance of disease. 



This leads me to offer a few remarks on parasitical fungi which are 

 destructive to agricultural plants. Those who have attended to the 

 subject must be aware that some of the most distinguished investiga- 

 tors of the cause of the potato-disease, consider this minute mould, 

 Botrytis infestans, to have been the immediate cause of the murrain 

 of last year, and, no doubt, it has very generally accompanied it both 

 in this country and on the continent. Its appearance on diseased 

 plants this season, is, therefore, the more remarkable. I can, however, 

 state with confidence, that two of the plants on which I have observed 

 It, were diseased long prior to the appearance of the fungi on the 

 Vol. II. 3 y 



