This section is from the book "The Gardener's Monthly And Horticulturist V18", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
Prof. Brainard, Chairman of the Scientific Committee, read a paper on Pear Blight.
After an elaborate discussion of plant growth, he said: "The green and tender portions of the tree are made up of cells, whose membranous walls are very thin and delicate; consequently, when the sap, with which these walls are always filled, is subject to sudden expansion, from either high or low temperature, the cell walls are ruptured and the sap runs out. A putrefaction condition soon follows, giving rise to fungoid growth, if other conditions are favorable.
"There are two causes that produce the rupture of these newly formed cells, and their action is very sudden and certain. These are extremes of heat and cold.
"In the spring of 1875, in Ohio and along the lake shore fruit region, after the trees had put forth their leaves, a sudden fall of temperature from summer heat to from 12° to 15° below freezing killed outright nearly every pear tree in that extensive fruit district. I examined many of these trees soon after, and found the external appearance exactly similar to what is called fire-blight.
" In order to test the influence of heat in producing the blight, I have subjected a vigorous and healthy.branch of a pear tree to an artificial heat of 108° Far., for 20 minutes. The effect upon the leaves and soft wood was vastly like the natural blight.
"The normal heat for the fruit-producing season ranges from 65° to 85°, the mean of which is 70°. A temperature of 95° is dangerous, and 100° and higher is disastrous.
"From careful observation and inquiry, I have found the trees upon a southern exposure much more liable to blight than those on a northern or north-eastern exposure."
The Prof, then gave several examples to sustain his position. "A gentleman has a pear orchard near the city, which has a northern exposure. This orchard has not been affected by the blight, while trees in the vicinity with a southern exposure have been completely destroyed. Another had pear trees on a southern exposure which were troubled with the blight. These he removed to a northern exposure, and they soon became healthy and fruitful, and no blight has since affected them. etc. etc.
" Keep your trees low-headed, and plant with a northern exposure, and you will take the most important measures to prevent the pear blight."
[We always give our correspondents free scope,-and of course are not responsible for their opinions. The effort of Prof. Brainard to ascertain the cause of pear blight by experiment, will attract attention at once, as the majority of those who profess to understand the disease will write for a year in preference to observing for an hour. In regard to the experiment itself, the fire-blight does not commence in the "leaves and soft wood," so that the analogy goes for nothing. Fire-blight commences in spots on the bark, often extending round the whole stem and girdling it - and not unless it does extend round and girdle the branch is there any injurious effect on "leaves and soft wood." The line between the healthy and unhealthy part is often so distinct as to be drawn by a hair line, and it is inconceivable that say one inch of bark should be injured by 108°, and an inch adjoining, separated but by a line, should be under the same temperature, and yet absolutely uninjured. The whole course of the Professor's argument, as well as of many other recent writers on fire-blight on the apple and pear, shows that he is thinking of some other disease than fire-blight, or else has given the appearances in the real disease, but a very cursory examination. - Ed. G. M.]