ON POTATOES. 185 



seen the leaves and stems of a crop, in a very low situation, completely 

 destroyed as late as the 13th of June, and they are generally injured 

 before the middle, and sometimes in the first week of September. 



The Irish varieties, being excessively late, are almost always killed by 

 the frost whilst in full blossom ; when omitting all consideration of the 

 useless expenditure of manure, it may justly be questioned whether the 

 tubers of such plants, being immature, can afford as nutritive, or as 

 wholesome food, as others which have acquired a state of perfect 

 maturity. 



The preceding statement will, I trust, point out to the Horticultural 

 Society the importance of obtaining improved varieties of the potato, 

 and I believe no plant existing to be more extensively capable of improve- 

 ment, relatively to the climate of England ; and if practical evidence 

 were wanted to prove the extent, to which the culture of the potato is 

 calculated to increase and support the population of a country, Ireland 

 most amply affords it ; where population has increased amongst the 

 Catholic poor, with almost unprecedented rapidity, within the last 

 twenty years, under the pressure of more distress and misery, than has 

 perhaps been felt in any other spot in Europe. 



1 shall conclude my present communication with some remarks upon 

 the origin and cure of a disease, the Curl, which a few years ago destroyed 

 many of our best varieties of the potato ; and to the attacks of which 

 every good variety will probably be subject. 



I observed that several kinds of potatoes, dry and farinaceous in their 

 nature, which I cultivated, produced curled leaves, whilst those of other 

 kinds, which were soft and aqueous, were perfectly well formed ; whence 

 I was led to suspect, that the disease originated in the preternaturally 

 inspissated state of the sap in the dry and farinaceous varieties. I con- 

 ceived that the sap, if not sufficiently fluid, might stagnate in, and close, 

 the fine vessels of the leaf during its growth and extension, and thus 

 occasion the irregular contractions which constitute this disease ; and this 

 conclusion, which I drew many years ago, is perfectly consistent with the 

 opinions I have subsequently entertained, respecting the formation of 

 leaves. I therefore suffered a quantity of potatoes, the produce almost 

 wholly of diseased plants, to remain in the heap, where they had been 

 preserved during winter, till each tuber had emitted shoots of three or 

 four inches long. These were then carefully detached, with their fibrous 

 roots, from the tubers, and were committed to the soil ; where having 

 little to subsist upon, except water, I concluded the cause of the disease, 

 if it were the too great thickness of the sap, would be effectually removed ; 



