304 
is, I believe, generally admitted to be the medium by which they prevail. 
and are carried from place to place. What that subtile principle may be, 
which pervades onr atmosphere, by which infection is retained and trans- 
mitted, so that, hke the Asiatic cholera, it makes the whole circuit of our 
earth, human science has not discovered; but that such a principal exists is 
sufficiently obvious from its effects.” There is ‘‘good reason to believe the 
vegetable world may be affected in like manner” with the animal. 
To this A. J. Downing appends an editorial note in which he states that 
the theory of Mr. Gookins of ‘‘an epidemic conveyed by the atmosphere” is 
‘too slightly supported by facts to weigh at all against the observations 
made by cultivators,” all of which ‘‘strongly points to the freezing of the 
sap as the cause.” ‘Were the cause atmospheric, its effects would always 
be seen first at the points of the shoots.” ‘Its first symptoms also would 
always develop themselves in the growing season.” On the contrary, the 
first symptoms of the frozen-sap blight are the black spots on the bark of the 
limbs or trunk, a long way from the extremities, and first seen in late 
autumn, winter or early spring. Repeats advice to prevent injury by white- 
washing the trees. 
1847. Barry, Patrick. (Rochester, N. Y.) [Editorial 
comment.] Genesee Farmer, vol. vim, 1847, p. 218. 
[2 col. ] 
“Insect blight” is more prevalent in some sections of the country this. 
season than it has been for the last seven years. Apple, pear, quince, crab, 
and even the walnut and hickory have all suffered. First noticed in the 
latter part of may, as the apple was passing out of bloom. Last of July it. 
is not abated. Generally'called ‘fire blight,” but believed by the writer to. 
be solely due to an insect that is venomous to the tree. Fruit spurs on apple: 
and pear attacked, afterward the extremities of the young newly formed 
wood. If cut away below the affected part, it is arrested. In apple and 
quince it proceeds but a foot or so below the point attacked, but in pear 
passes downward rapidly until the tree is dead. This is like the ‘‘frozen- 
sap blight,” so much talked of at the West. Sap becomes brown and thick, 
the bark cracks and blackens and turns hard as iron. Attacks healthy trees 
on dry land, noticeably fruiting trees largely, including Seckel. Other 
reasons are given for believing it due to an insect, but not to Scolytus pyri, 
yet the writer has found no track of the insect even with a lens. 
1848. Ernst, A. H. (Cincinnati, O.), and A. J. Downing: 
On the fire blight in pear trees [| with comments]. Hort., 
vol. 1, 1848, p. 328. [31 pages. ] 
Lowell’s insect theory and Downing’s frozen-sap theory are thought inad- 
equate, and ascribes it to the heat of the sun, assisted by rain drops acting 
as lenses. The effect is to ‘‘scald the sap, burst their vessels, and produce: 
precisely the same results that a scorching fire would.” The argument is. 
well presented. The remedies suggested are to select varieties with wood: 
‘of a compact texture and slow of growth,” like the Seckel, and give north- 
ern exposure. The editor, A. J. Downing, believes this explanation correct 
for certain forms of blight, other forms are produced by insects, and others. 
still by freezing. 
1848. Harris, T. W. (Cambridge, Mass.), and A. J. Down- 
ing. On the blights of the pear tree [with comments]. 
Hort., vol. 1, 1848, p. 365. [24 pages. | 
A strong argument, to show that the insect blight, produced by Scolytus: 
pyri, which does not seem to be known in the Western states, is entirely dis-~ 

