"It is well established, then, that a number of diseases of the animal system are produced by fungi. 'Under this name botanists comprehend not only the various races of mushrooms, toadstools, and similar productions, but a large number of microscopic plants, forming the appearances called mouldiness, mildew, smut, rust, brand, dry rot, etc.' They are universally diffused in nature. It is difficult to conceive of a place where they do not exist. They are among the most numerous of all plants, in regard to genera and species, and with very few exceptions are deleterious in their impressions on the animal system. Even the palatable mushroom is always poisonous to some persons, and may become so to all under certain circumstances. It is equally evident that fungi frequently occasion diseases in the vegetable kingdom. The smut of wheat and maize, the rust of wheat, ergot of rye and grass-seeds, and specks, cracks, and discoloration of the skin of the apple and pear are of this nature.
"The microscopical examinations of Prof. Salisbury and others have detected the presence of certain species, infesting extensively pear trees about the period of attack by the blight. They have made similar discoveries that lead to the conclusion that the curl of the peach leaf, the potato disease, and the blight of pear trees, all have their origin from the cause assigned in my second proposition.
"Under this head still another disease of our fruit should be noticed. I have watched carefully the sudden and premature decay of our plum crop, at the period of its ripening, for the last fifteen years. From hints afforded by the work of Prof. Mitchell, and several microscopic observations of my own, I was induced to publish an article in 'The Florist,' of Philadelphia, in the year 1855, in which I imputed the origin of the disease to the Torula or some analagous species of parasitic fungi. The disease still prevails among us, and it is sure to destroy all the plums which escape puncture by the curculio. It is, however, generally overlooked by pomologists, and its effects are charged to the depredations of that insect. Similar disease occasionally impairs our peach and apple crops, to a less extent. Whenever it occurs on either of these varieties of fruit, the spurs and young wood blight or canker, and cease to be fruitful for several years.
"If these discoveries and analogies establish, with any degree of certainty, the hypothesis of the cryptogamous origin of the pear tree blight, we have made important progress in laying down true indications for its cure or prevention. Among the means suggested for effecting that end, certain combinations of iron have already been named. The authority for such practice is founded on the following facts:
"1. It is a popular belief that iron exerts a favorable influence over the health of fruit trees. Hence arises the practice of driving nails into the body of such trees, and loading their limbs with scraps of iron. Both the belief and the practice may be visionary, yet in such instances of popular belief, investigation usually discovers them to be founded on some shadow of truth.
"2. An intelligent and observing gentleman of Cleveland informs me that he prevents the curl of the peach leaf by depositing in the earth, about the bodies of the trees, fragments of rusty stove pipe and worthless pieces of iron.
"3. Twenty-four years since I called the attention of the public to the isolated fact, without reference to any theory, that a large pear tree in Columbiana county, Ohio, with its body surrounded with many wagon loads of boulders, scoria, scales of iron and accumulations from a blacksmith shop, retained its health, vigor, and fruitfulness, while all other pear trees in that region of country had either died, or were suffering from blight. Vide New England Farmer, December 3, 1840, page 153. At this late day this tree still continues healthy.
"4. I recollect reading in that reliable journal, Hovey's Magazine of Horticulture, some years since, a statement that the finest prize pears seen in the Parisian market, were produced by investing the growing fruits with folds of cotton or linen cloth, and daily, or oftener, moistening them with a solution of sulphate of iron. This treatment was said to result in developing the size, beauty, and quality of the fruits to a high degree, and especially to free them from parasitic blotches.
"5. Four years since, Mrs. Weller Dean, of Rockport, Ohio, informed me that blight might not only be prevented in healthy pear trees, but might be successfully arrested, in many trees, after it had made considerable progress, by means of repeatedly washing the bodies of the trees with a saturated solution of sulphate of iron (copperas), at a time when the sap is in active circulation.
"This was a confidential communication, with the condition annexed that I should thoroughly test the plan, and if it should prove successful, I was to publish it; and furthermore, if any merit or more substantial reward should be deemed due to any one by the public, she was to be the recipient.