DECLINE OF PLANTS. 



I am doubtful whether T shall not be trespassing too much on the patience of your read 

 ers, by recurring again to this subject; but the question I conceive has a great practical 

 bearing, and if the view I now send you, of the effects of age, should prove on further in- 

 vestigation, to be well founded, the most sceptical can hardly be otherwise than convinced, 

 because of the exact and conclusive evidence it will afford of the truth of Mr. Knight's 

 conclusions, respecting the limited duration of varieties of plants propagated by exten- 

 sion. 



It would seem that the potato, in the earlier 3'ears of its culture in Europe, was either 

 entirely or comparatively free from disease. The first notice I have met with of the 

 " curl," (a disease so called from the leaves contracting or curling, instead of expanding,) 

 is in a paper in the Transactions of the London Society of Arts; wherein it is said, that 

 the disease was probably first noticed in Lancashire, about 17G4; about that time a man 

 observed a few plants in his crop which decayed, or seemed to ripen sooner than the rest, 

 and he straightway concluded that somehow he had luckily obtained a new and early kind; 

 he accordingly marked the plants with a view to cultivate them, but was much disappoint- 

 ed and perplexed by the result of his experiment. Baron Hepburn, in a communication 

 to the Board of Agriculture, said the curl was unknown in Scotland before the years 1778 

 or 1779. Dr. Anderson, in an essay on the potato, in the Bath Papers, remarked, that 

 the onl}'- thing which seemed to be positively certain with regard to curl, is, that it was not 

 known in the northern parts of the country, till a very few 3'ears ago, and at that time it 

 was much less prevalent in the north than in the south. 



Towards the close of the 18th century, the curl prevailed in the potato crops to such an 

 extent, as to give rise to much discussion, and many experiments, with a view to discover 

 the cause of the malady, and by what means it could be prevented. 



Manj' observations might be cited to prove that this first mild form of disease of the 

 potato, could not be attributed solely to any peculiarity of soil, season, or mode of cul- 

 ture, but that it was peculiar to, and therefore inherent in, certain varieties for the time 

 being. I learn ffom two prize essays in the Transactions of the Society of Arts, for 1790, 

 that it was known at that time, that certain varieties only were subject to the disease; 

 that it was hereditary, and that the only effectual mode of getting rid of the evil, was by 

 discarding the affected varieties. One of the writers, Mr. Pitt, said, " the curl in pota- 

 toes is doubtless owing to degeneracj' — to the particular varict}^ being worn out. I have 

 known three to fail by curling in this county, (Staffordshire.) The national remedj^, 

 therefore, is, the raising and reproducing fresh varieties, a practice which has never been 

 interrupted by any difficulty." Mr. Holt, who wrote from the neighborhood of Liverpool, 

 observed, " the cause of the disease, so far as lean learn, appears to be nothing more than 

 a degeneracy of the plant. This district, for some years, suffered great injury from curled 

 potatoes, but few crops of late years have failed of being much infected with this disorder, 

 for whenever the curl has appeared, in ever so small a digree, that stock has been rejected 

 by the attentive cultivator, and new seed obtained." Hence the conclusion based on these 

 facts, as we read in Martyn's edition of Miller, " the circurast;mces of the old sorts being 

 now almost entirel}' cut off by curl, renders it probable that the disease is incident to de- 

 clining varieties of potatoes, as canker is to declining varieties of fruit." 



About the time the curl was so prevalent in England, it seems to have prevailed to a 

 considerable extent on the continent of Europe, also. A reward of 1,200 francs was of- 

 fered in 1775, by the Royal Academy of Brussels, for the best treatise on the cause of the 

 disease. The prize was awarded to a writer who concluded that it was the resu 

 degeneracy of tlie plant, owing, as he supposed, to its being an exotic. He advised 



