— 4 — 
and some on pure conceptions of the mind. Every theory 
as to the cause prescribed a remedy based upon the theory. 
These remedies were put to trial and reported on; reports 
varied. Two men would report the use of a remedy under 
similar circumstances; one with favorable results, the other 
with adverse results. The next season the same men using 
the same remedy in the same way would reverse their re- 
ports. Success one year would be counterbalanced by 
failure the next, and the remedy would be laid aside as 
useless. 
Many of the successes with various remedies as reported 
in the older journals, we can now see were simply successes 
reasoned from negative results. A man has a tree affected 
with blight, he cuts off the blighted limbs, applies a wash of 
copperas over the tree, the blight progresses no further, 
and he reports a cure effected by washing with copperas. 
His experiment is worthless; had he allowed the blighted 
branches to remain on the tree, and applied the copperas, 
with an arrest of the disease as a result, then his report 
would have been warranted. But as he reported, might not 
his accredited cure have been due to the complete removal 
of the disease with the infested branches which he cut off? 
And just so with a great number of experiments tried with 
other remedies. They were of no value because conclusions 
were hastily drawn from only a part of the attending cir- 
cumstances. 
THEORETICAL CAUSES. 
Among the numerous assigned causes of pear-blight I 
may mention the following. i-Electricity and atmostpheric in- 
fluences. 2-A stroke of the sun. 3-Old age, or a long 
duration of varieties. 4-A sudden freezing of the bark. 
5-The freezing of the roots wherby absorption is prevented, 
and, the supply of moisture being cut off, the evaporation 
from the branches caused blight. 6-Too high culture. 7- 
The absence of certain mineral matters in the soil. 8-In- 
sects. g-Eungi. lo-An epidemic transmitted from place 
to place by the air. 
Each of the above theoretical causes had a following, 
but most of them were entertained for a brief period only, 
because observed facts made the theories untenable, and 
wherever any one of these theories was put to the test of 
actual experiment it was quickly shown to be fallacious. 
Downing’s frozen-sap theory. 
The most widely accepted of the early theories was that 
