446 The Blight in the Pear Tree ; 



around the whole triinkl Now here is a striking appear- 

 ance of the great bHght, confounded with the minor bhght, 

 as I think will appear in the sequel. 



This theory has stood in the way of a discovery of the 

 true cause of the great blight ; for every cultivator has 

 gone in search of insects; they have been found in great 

 plenty, and in great variety of species, and their harmless 

 presence accused with all the mischief of the season. A 

 writer in the Farmer s Advocate^ Jamestown, JN. C, dis- 

 cerned the fire-blight, and traced it to " small, red^ pellucid 

 insects, briskly moving from place to place on the branch- 

 es." This is not the ScolytKs jajri of Prof. Peck and Dr. 

 Harris. 



Dr. Mosher, of Cincinnati, in a letter published in the 

 Farmer and Gardener for .Tune, 1844, describes a third in- 

 sect, — " very minute broimi- colored aphides^ snugly secreted 

 in the axilla of every leaf on several small branches; * ^ 

 most of them \v*re busily engaged with their proboscis in- 

 serted through the tender cuticle of this part of the petiole 

 of the leaf, feasting upon the vital juices of the tree. The 

 leaves being thus deprived of the necessary sap for nour- 

 ishment and elaboration, soon perished, * * while all that 

 part of the branch and trunk below, dependent upon the 

 elaborated sap of the deadened leaves above, shrunk, turned 

 black, and dried up." — p. 261. 



Lindley, in his work on Horticulture, p. 42-46, has de- 

 tailed experiments illustrating vegetable per^yj/rcf^io;?, from 

 which we ma^^ form an idea of the amount of fluid which 

 these "very minute brown-colored aphides" would have to 

 drink. A sunflower, thrfee and a half feet high, perspired 

 in a very warm day thirty ounces — nearly two pounds; on 

 another day, twenty ounces. Taking the old rule, "a pint 

 a pound," nearly a quart of fluid was exhaled by a sun- 

 flower in twelve hours; and the vessels were still inflated 

 with a fresh supply drawn from the roots. Admitting that 

 ihe leaves of a fruit tree have a less current of sap than a 

 sunflower or a grape vine, yet in the months of May and 

 June, the amount of sap to be exhausted by these very mi- 

 nute brown aphides, would be so great, that if they drank 

 it so suddenly as to cause a tree to die in a day. they 

 would surely augment in bulk enough to be discovered 

 without a lens. If some one had accounted for the low 

 water in the Mississippi, in the summer of 1843, by saying 



