414 BOARD OF AGRICULTURE. 



sward to high tillage. And the result is stated to be an "overplus" of 

 sap, or a "surfeit." All these causes occur every year, but the blight does 

 not every year follow them. Changes of temperature and violent condi- 

 tion of the soil may be allied with the true cause. But when only these 

 things exist, no blight follows. 



4. Others have attributed the disease to ovea- stimulation by high 

 manuring or constant tillage, and it has been said that covering the roots 

 with stones and rubbish, or laying the orchard down to grass, would pre- 

 vent the evil. Facts warrant no such conclusions. Pear trees in Gibson 

 County, Indiana, on a clay soil, with blue slaty subsoil, were affected 

 this year more severely than any of which we have heard. Pears in 

 southern parts of this State, on red clay, where the ground had long been 

 neglected, suffered as much as along the rich lands of the Wabash about 

 Vincennes. If there was any diffei-ence it was in favor of the richest land. 

 About Mooresville, Morgan County, Indiana, pears have been generally 

 affected, and those in grass lands as much as those in open soils. Aside 

 fi'om these facts it is well known that pear trees do not blight in those 

 seasons when they make the raugest growth more than in others. They 

 will thrive rampantly for years, no evil arising from their luxuriance, and 

 then suddenly die of blight. 



5. It has been supposed by a few to be the effect of age, the disease 

 beginning on old varieties and propagated on new varieties by contagion. 

 Were this the true cause, we should expect it to be most frequently de- 

 veloped in those regions where old varieties abound. But this disease 

 seems to be so little known in England that Loudon in his Encyclopedia 

 of Gardening does not even mention it. Mr. Manning's statement wiU be 

 given farther on to the same purport. 



6. Insect Theory.— The confidence with which eastern cultivators pro- 

 •Jiounce the cause to be an insect, has in part served to cover up singular 



discrepancies in the separate statements in respect to the ravages, and 

 even the species of this destroyer. The Genesee Farmer of July, 1843, 

 says, "the cause of the disease was for many years a matter of dispute, 

 and is so still by some persons; but the majority are now convinced it is 

 the work of an insect (Scolytus pyri). T. W. Harris, in his work on- 

 insects, speaks of the minuteness and obscure habits of this insect, as 

 "reasons why it has eluded the researches of those persons who disbelieve 

 in its existence as the cause of the blasting of the limbs of the pear tree." 

 Dr. Harris evidently supposed, until as late as 1843, that this insect in- 

 fested only the pear tree, for he says, "the discovery of the blight-beetle 

 in the limbs of the apple tree is now a fact in natural history, but it is 

 easily accounted for, because this tree belongs not only to the same 

 natural group, but also to the same genus as the pear ti'ee. It is not, 

 therefore, surprising that both pear and apple tree should be attacked by 

 the same insect." (See an article in the Massachusetts Ploughman, sum- 

 mer of 1843, quoted in Genesee Farmer, in July, 1843.) ' 



