130 ANNUAL REPORT. 
through them. The most of the trees are dead, root and branch. When 
the diseased condition was at its worst in June, an unpleasant odor was 
wafted on the breeze to a considerable distance. The grafts planted last. 
spring arefall right. An older nursery, somewhat neglected, and covered 
last season and this with a growth of weeds, is but little affected. I have 
thought it possible that too rapid growth had something to do with it, but 
if so, why do our orchards in Bluegrass sod blight so badly? The crabs. 
were the first to blight. Please give us such light as you can.” 
On page 168 of the Iowa Horticultural Report for 1877, the writer pre- 
sents the results of long-continued observation and experiments, supporting 
the idea that our excessive heat of soil and lower beds of air in orchards on 
dark-colored, exposed soils, is a probable cause of this and other orchard 
troubles. TheyFrench gardeners talk of ‘‘ coup de chaleur”—stroke of heat— - 
in connection with apple, pear, and plum trees becoming diseased, when 
standing on the sunny side of high walls where the reflection of the sun’s 
rays creates an abnormally high temperature within the tree. The great 
French physicist, Mr. Becquerel, records, as the result of carefully con- 
ducted experiments, that an internal temperature of the plum tree of 98 
degrees Fahr., in August, when the cells of the newly-formed wood.deposit 
are becoming solidified and freed from watery particles, always results in 
diseased condition of the tree, and usually in death within a short time. In 
other words, he found that a temperature of sap-wood exactly favorable to 
most rapid growth of semi-tropical plants, would produce disease in, and 
death of trees indigenous to the north. We also agree that our varieties of 
the apple from Siberia, and their crosses retaining the Siberian form, are 
first to exhibit traces of the blight. They are capable of enduring our test 
winters, but they know nothing in their native country of our summer-heat 
of soil and air. The varieties of the apple we receive from the interior of 
Russia, with the thickened epidermis of leaf and bark developed in the 
course of generations by their dry, hot summurs, are Jess subject to blight, 
even in positions where they must endure a temperature some higher than 
is natural. Our varieties imported from England, or other portions of 
southern Europe with cool, moist summers, as we might expect, are variable 
as to their capacity to endure our summers or our winters, just as their 
structure is varied by their origin. 
The idea is perfectly illustrated by the varieties and behavior of the wheat. 
plant in various portions of the world. In more equable and regularly 
humid climates the forms of disease engendered by our arid summer-heats 
are unknown, while at Xalapa, Mexico, ‘‘ wheat will not mount into ear, but 
produces a low-growing grass.” Lindley lays down the axiom in Horticul- 
ture that ‘all plants require the soil as well as the atmosphere, in which 
they grow to correspond in temperature with that of the countries of wuich 
they are native.” Yet he devotes a large part of his ‘‘ theory and practice 
of Horticulture” to the means at the command of the gardener for the 
modification of natural conditions of soil and air by artificial means. 
In our orcharding we cannot modify soil and air conditions as we do with 
glass structures, shading, etc., with our flowering plants, but by selection of 
varieties, position, and treatment of surface soil of our orchards, we can 
control the summer temperature of our trees sufficiently to exempt us from 
serious trouble in the way of blight. As an instance of surface modification, 
