DECLINE OF PLANTS. 



new varieties should be obtained from Virginia, the potato being supposed at that time to 

 be indigenous to that country. Ilis advice was followed, and the remedy proved efficient. 

 So the Belgian, like the English cultivators, found that the most effectual, or only certain 

 means of restoring their crops to health, was by substituting healthy varieties for those 

 which were subjected to the disease. 



Many well-informed men have concluded that curl is caused by the over-ripening of the 

 seed tubers, and the Aicts are certainly too numerous, and too well authenticated, to ad- 

 mit of doubt, proving that the state of ripeness, or rather the dry condition of the tuber, 

 does exercise a considerable influence on, if it is not the immediate cause of the curl. 



The authors of several of the earlier papers for instance, observed, that when the curl 

 was rife among the crops in rich, low-laying, early soils, it had never been experienced in 

 neighboring hilly districts, having a northern aspect, where vegetation was more backward, 

 and where the crops had not the same chance of becoming perfectly ripe. It was also fre- 

 quently observed, that curled plants proceeded from large, hard tubers, which did not de- 

 cay in the ground, as usually happens. Others had noticed that small potatoes, which had 

 been thrown aside for pigs, but which were planted for the want of a sufficient number of 

 sets of larger potatoes, droduced entirely healthy, smooth-leaved plants. 



The expedients which at various times have been resorted to with a view to prevent the 

 disease, such as by obtaining the seed-tubers from late situations, or by raising them be- 

 fore the haulm had naturally decayed, or by planting late in the season, so that they could 

 not have time to ripen, all indicate that under-ripe watery tubers afford the most healthy 

 and vigorous plants, and some security against the disease. 



The influence of the dry state of the tuber in producing curl, has also been proved ex- 

 perimentally. Sets taken from the waxy, or least ripened end of a long kidney potato 

 subject to curl, were found to produce healthy plants; whereas, sets from the opposite 

 dry end of the same tubers, did not vegetate at all, or produced curled plants. Mr, Kkight 

 conceived that curl originated in the preter-naturally inspissated state of the sap, and he, 

 from a number of tubers, the produce of wholly diseased plants, carefully detached the 

 shoots when about three or four inches long, and planted them; as they had now little to 

 subsist upon, except water, not a single curled leaf was produced, though more than nine- 

 tenths of the plants which the same identical tubers subsequently produced, were much 

 diseased. 



There can hardly be any question, then, that curl is in some wa}' induced by the per- 

 fectly ripe or dry state of the seed-tubers. But then it seems equally certain that the po- 

 tato was formerly free from this disease, and that varieties do not become subject to it till 

 they have been some time in cultivation. Sir John Sinclair, in his work on the potato, 

 said, "if continued too long, they are liable to disease, as the curl." Sheriff, an emi- 

 nent Scoth farmer, observed, " time or old age, never fails ultimatelj" to bring on the curl- 

 ed or shriveled disorder." How are these seeming inconsistencies to be reconciled? Either 

 the potato formerly, or varieties in the earlier 3'ears of tjieir existence, never ripened their 

 tubers, or perfect ripening alone is not sufficient to account for this disease. There must 

 be some other undiscovered agent at work, which has power over those plants onl}^ that are 

 the produce of ripe tubers of aged varieties; or else, in the progress of time, a change takes 

 place in the tubers of a given variety; the texture must become more solid, the fluids 

 thicker and less abundant, and therefore incapable of sujiporting healthy vegetation. 



A given species of plant requires a certain range of temperature, and a certain amount 



ht, to enable it to grow in a healthy and profitable condition. The Palnis of the tro 



ill not grow to any useful purpose in the United States; nor will our apple trees 



