"These publications attracted the attention of the medical profession, both in America and Europe, so long as that epidemic continued its ravages, and the theories they advanced gained extensive credence during that time. They were, however, lost sight of when that epidemic subsided. Recently they have been substantiated as plain matters of fact, so far as malarious diseases are concerned, by the labors and investigations of Prof. J.H. Salisbury, of Cleveland.

"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, s.m.u.t, 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 circ.u.mstances. It is equally evident that fungi frequently occasion diseases in the vegetable kingdom. The s.m.u.t of wheat and maize, the rust of wheat, ergot of rye and gra.s.s-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 a.s.signed 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. Mitch.e.l.l, 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 a.n.a.lagous 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 a.n.a.logies 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 sc.r.a.ps 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 acc.u.mulations 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.

"This plan has yet been only imperfectly tried. Age and infirmities will probably prevent its completion by me. I will therefore report that I have tested it on a number of my partially blighted pear trees, while a greater numbers has been left to die unmedicated. Of the former, not one has yet perished, while of the latter very few survive. It has appeared, in every instance, to arrest the progress of the disease, and to impart a healthy condition to the bark wherever applied. The apparent results may have been coincidences and not the effect of the remedy. There is much false experience in horticulture and agriculture, as well as in medicine.

"These views suggest the expediency of extensively applying a solution of the sulphate of iron by means of a green-house syringe or garden engine to the tops and foliage of trees, laboring under any of the diseases suspected of a cryptogamous origin. It also becomes a query whether the same agent may not be successfully employed at some period to counteract the potato disease, either by watering with it the growing plant, or washing the tubers in it in autumn, after they are dug. No injury has ever arisen to pear trees by a free use of a _saturated_ solution of copperas.

"In conclusion, I would observe that the discovery of the cryptogamous origin of the many disorders of the human system is effecting important changes in their treatment. May we not hope that an extension of these discoveries to the vegetable kingdom, may result as favorably in shaping the practice in diseases of fruits and fruit trees?"

4th--Wounds, and the attacks of insects, may be considered more in the light of mechanical injuries by a loss of substance, hence they belong rather to the department of surgery, and can scarcely be considered as disease. The breaking of a branch, or the removal of a portion of the bark, may inflict a serious injury, but it is one which, under ordinary circ.u.mstances, will be recovered from, without any impairment of the health of the tree--unless where the wound is so large that the new growth will not soon cover it over, in which case exposure to the moisture of the atmosphere may result in decay of the woody tissues, or, if the sap exudes, at certain seasons, it may produce canker and fungous growths. In some varieties of our cultivated fruits, wounds of this character are often attended by an effusion of gummy matter; this is particularly the case with those that are known as stone-fruits, and in these the excision of a large limb is seldom followed by a deposit of woody matter in the way of healing over the wound, which is always desirable; hence in such cases particularly, it is well to cover the exposed surface with something to exclude atmospheric moisture, whether this be paint, varnish, of sh.e.l.lac, or common grafting wax.

Insects, by eating the foliage extensively, very materially injure the healthy condition of a tree--even the minute aphides that suck the sap from the leaves and tender bark, will seriously impair the health of our plants; but the borers that mine under the bark, extensively consuming the vital cambium, and even burrow into the solid wood, reducing it to a honeycomb, cannot fail to affect the healthy condition of the tree materially, and often cause its premature death.

Some knowledge of the habits of these little creatures is considered of so great importance, that the subject will be brought before the reader's notice more at length in another part of this volume.

There is no doubt, however, that many unhealthy conditions of our trees, that might be traced to other causes, but which are not manifestly dependent upon a want of care on the part of the orchardist, nor upon a deficiency in the const.i.tution of the soil, are often attributable to the inroads of these minute foes, which, in some cases at least, are made the scape-goats upon which is laid the blame that should be applied to our own neglect, or want of forethought and care.

After having reviewed the whole subject, it may be safe for us to conclude that what is called disease in our cultivated vegetables of whatever kind, is a departure from full health and productiveness of sound fruits. And further that this may arise from a lack of the necessary ingredients in the soil, from a want of proper conditions as to its quality and const.i.tution, particularly with regard to the important elements of moisture, heat, and light; and especially, that this condition of unhealthiness and unproductiveness, when not an inherent failing of the variety, may in many instances be attributable to want of proper care on our part, and to our allowing the trees to injure themselves by overbearing, while we neglect to keep up the proper supply of nourishment.

In making selections of trees for planting, it is important that all weak or unhealthy varieties should be avoided. Secure healthy and vigorous stocks, that appear to be possessed of a sound const.i.tution, even though the fruit should not be quite so fine and beautiful as that produced by some of the sickly and less vigorous varieties. There is more difference apparent, in this respect, among pears than among apples; but of the latter there are varieties that should be avoided on account of their deficient vigor. There are others that might be considered as coming under the ban, because the trees are not long-lived; and yet some of these appear to be perfectly healthy in every other respect, and seem literally to wear themselves out by excessive bearing, producing annual crops of large and handsome fruit, until, utterly exhausted, they reach a premature end.

Some varieties, that for many years yielded very fine crops of the most beautiful fruit, and of the highest character for flavor, have afterward ceased to furnish any perfect specimens--the whole crop being covered and deformed with the black scab or fungus, that prevents their development, or else ruined by the disagreeable bitter-rot which entirely spoils them for any use. Various remedies have been suggested for these maladies, all of which are more or less unsatisfactory, because from our ignorance of the causes of the troubles; these applications are wholly empirical.

The Black-knot, which has become very common in some parts of the country, is well discussed by Benjamin D. Walsh, in the Practical Entomologist, for March, 1866, page 48.

This essay is the more valuable because of the absence of the empiricism just complained of:--

"It is a black, puffy, irregular swelling on the twigs and smaller limbs of plum and cherry trees, and, in one instance that came under my personal observation of peach trees, making its first appearance in the lat.i.tude of New York early in June, and attaining its full growth by the end of July. Usually a tree, that is attacked in this manner, is affected worse and worse every year, until it is finally killed; and wherever one tree of a group is affected, the malady usually spreads to them all in process of time. In 1865 whole cherry orchards were destroyed in Western New York by this disease, and I have myself seen many groups of wild plum trees in Illinois that were gradually perishing by it; but in Southern Ohio, as I am told, the Black-knot is never met with. In the Eastern States it has been observed from time immemorial, and various contradictory opinions have been broached as to its real nature and origin.

"In 1865 I watched the Black-knot carefully through all its stages, from its earliest commencement to its complete maturity, experimenting at the same time on numerous specimens collected week after week, so as to ascertain what insects bred in it. The practical conclusion I have arrived at, is simply this:--_If the diseased twigs are all cut off and destroyed early in July in the lat.i.tude of New York, or a little earlier or later according to the lat.i.tude, taking care to cut a few inches below the affected part, the Black-knot can be checked and probably entirely eradicated; but if this operation is delayed till August, it will be of no benefit whatever._ Hence we can easily account for a circ.u.mstance which has puzzled many men wonderfully, viz.: That cutting off and burning the diseased twigs is p.r.o.nounced by some to be a sovereign remedy, and by others to be a delusive humbug.

Those that do this early enough, find it effectual; those that delay it till too late, find it of no use.

"This perhaps will be sufficient for some few impatient souls, who take everything upon trust that they see in print, and care nothing about the _rationale_ of a mode of treatment, so long as it be practically available. But for the benefit of that large cla.s.s of intelligent agriculturists, who have been deluded by too many quack prescriptions to place much faith in any man's _ipse dixit_, and who in any case like to understand the principle of a remedy before they apply it, I subjoin a full account of all that is at present known on this subject, and of the different theories respecting it entertained by different writers.

"Three radically different theories have been broached as to the nature and origin of Black-knot: 1st, that it is a mere disease of the tree, like the cancer or the gout in the human race, which is the view maintained by Dr. Fitch, the State Entomologist of New York; 2d, that it is what naturalists term a "gall," produced by some unknown insect depositing its eggs in the twig--just as the well-known "oak-apples"

are produced by a Gall-fly, (_Cynips_), depositing its egg in the bud of the oak--which is the opinion that I myself formerly held and maintained, before I had fully examined into the subject; (_Proceedings Ent. Soc., Phil._, III, p.p. 613-618;) and 3d, that it is what botanists term an epiphytous fungus, growing on the tree as a mushroom or toad-stool grows on the ground, which is the opinion of the botanist Schweinitz, and which has recently been re-a.s.serted by Mr. Glover, the Entomologist of the Bureau of Agriculture at Washington, (_Ag'l Rep._, 1863, p. 572.) This last is the opinion which, upon full inquiry, I have now adopted.

"Before discussing these theories, the facts arrived at by myself in the summer of 1865, must first be briefly noticed. It should be premised that the old, dry Black-knot remains on the tree for many years, and that the place to look for the new Black-knot is on such trees as have been already attacked and are loaded with old Black-knot, without being as yet completely killed by it.

"1st. By the middle of June the new Black-knot is pretty well developed, and may then be readily distinguished from the old by its dull, opaque, brown-black color, while the old is coal-black and more or less glossy. When cut into, it is found to be fleshy inside, like an apple, but not juicy, and of a pale greenish-yellow color, with fibres radiating from the axis of the twig, while the old Black-knot is internally hard and woody, and of a reddish-brown or rust-red color. The brown-black color of the external surface is retained till the last week in July, when the surface of the new Black-knot becomes gradually covered all over with little, coal-black, hemispherical plates, appearing when viewed through a pocket gla.s.s, about the size of the head of a pin, each of these is a distinct fungus, named long ago by Schweinitz '_Sphaeria morbosa_.' Even on the old Black-knot this fungus may be readily seen, at any time of the year, covering its entire surface. So far I have added little to the information already published on this subject, except by the specification of dates. But in addition to these facts, I discovered that about the last of July or the first week in August, there grows from each fungus on the surface of the Black-knot a little cylindrical filament about one-eighth of an inch long, which no doubt bears the seed or "spores,"

as they are technically termed, of the fungus, and that these filaments very shortly afterwards fall off and disappear, leaving behind them the hemispherical plates, which alone had been hitherto noticed by the botanists. In another Epiphytous fungus, which grows commonly and abundantly in Illinois on the Red Cedar, but which differs from the Black-knot in being attached to the twig by a very short stalk or peduncle, and in being roundish and externally of a reddish-brown color instead of elongate and black, there is a precisely similar phenomenon; except that the plates and filaments are very much larger, and that each filament, when it falls off, leaves a ragged scar behind it. In a single specimen of Black-knot noticed August 6th, I discovered that the filaments not only covered the entire surface of the Black-knot itself, except where a few of them had already fallen off, but that they were thinly studded over the twig for an inch or two above and below the swollen black part; thus proving that the fungus sometimes extends rather further than on a cursory view it would appear to do. Towards the middle of August, the new Black-knot, having perfected its seed, gradually dries up and becomes internally of a reddish-brown color. In other words, like so many other annual plants, it dies shortly after it has perfected its seed, just as a stalk of wheat or of corn dies shortly after the grain is ripe.

"2d. During the months of June and July I collected from time to time very numerous specimens of Black-knot, some of which I cut into to see what larvae they contained, and some I preserved to see what perfect insects could be bred from them. Besides seven specimens of the common "Curculio," which many persons had previously bred from Black-knot, I bred for the first time therefrom no less than five distinct species of insects, none of which can be considered as gall-makers, but not a single true gall-maker; and I can confirm Dr. Fitch's a.s.sertion, that some specimens are wholly free from larvae of any kind when cut into.

"We will now take up in order the three different theories respecting the nature and origin of Black-knot, which, as already stated, have been maintained by different writers.

"1st. _That Black-knot is a mere disease like the cancer._--Dr. Fitch, who maintains this opinion, allows that the black granules found on the Black-knot are a true fungus, 'that the surface of these excrescences, when mature, is always covered with this plant,' and that 'this plant never grows, or at least has never been found, in any other situation.' (_Address N.Y. State Ag'l Soc._, 1860, p. 21.) * * *

"2d. _That Black-knot is a gall._--As already stated, there is no true gall-making insect that inhabits the Black-knot, so far as I can discover on the fullest and most extensive investigation that I have been able to give to the subject. The minute holes commonly found in the old dry Black-knot, which are too large either for the 'Curculio'

or for the small moths bred by myself from Black-knot, are of a suitable size for either of the two dipterous' insects which I have enumerated in a note as bred by myself from Black-knot. Consequently the argument which I based upon the existence of these minute holes (_Proc. Ent. Soc. Phil._ III, p. 614) falls to the ground; and although I found on one occasion the larva of a Gall-gnat embedded in a cell in a Black-knot, yet this was most probably that of the Guest Gall-gnat which I actually bred from Black-knot, as stated in the note, and not of a true gall-making Gall-gnat.

"3d. _That Black knot is a fungus._--Just as Dr. Fitch, having proved to his own satisfaction that Black-knot is neither a gall nor a fungus, infers by the method of exhaustion that it must be a disease; so, having proved that it is neither a disease nor a gall, we may infer by the method of exhaustion that it must be a fungus, or rather an a.s.semblage of funguses. In confirmation of this theory may be adduced the very remarkable a.n.a.logies between the structure of the Black-knot and that of the fungus, described above as occurring on Red Cedar. That this last is really and truly a fungus and not a gall, is shown by the fact, that it is scarcely ever inhabited by insects; for out of hundreds of specimens that I have cut into, both green and dry, not more than two or three contained the larvae of the moths, but one contained what was probably the larva of an Ichneumon-fly, and all the rest were perfectly solid and unbored. On the other hand, Black-knot is so infested by insects, that it is almost impossible to find a mature specimen that is not all bored up by them. The cause of this remarkable difference may be attributed to the well-known repugnance of almost all kinds of insects for Red Cedar.

"If, then, Black-knot is a fungus, and if, as I think I have shown, it is an annual plant propagating itself by seed or the so-called 'spores,' and the 'spores' make their appearance about the end of July in lat.i.tude 41 30', then it must be obvious that if all the Black-knot on a particular tree is cut off and destroyed in the fore-part of July, or a little earlier or later as you go further south or further north, an effectual stop will be put to its further propagation. It is true that the 'spores' are in the form of an impalpable powder, so that they may be carried some considerable distance from other infected trees by the wind; and it may possibly be further true, that certain 'spores' may lie dormant in the bark for over a year, as the seeds of weeds will often lie dormant in the ground. Still, with all these possible drawbacks, I have little doubt that the above remedy will, as a general rule, if applied according to directions, be found effectual."

The foregoing is interesting as giving the conclusions of an entomologist who had investigated the subject, and arrived at the same result that had been reached by a botanist many years before.

Schweinitz, in 1832, published the correct history of the Black-knot in the Transactions of the American Philosophical Society. In the _American Agriculturist_, April, 1863, p. 113, Mr. C.F. Austin confirmed Schweinitz's observations, and gave a popular account of the botany of this fungus, with figures. It may be considered as fully established that the knot is of vegetable origin; and whenever insects or larvae are found in it, it is only because they find a diseased portion of the tree suited to their necessities.

ROT AND MILDEW upon the grape both destroy our crops, and render the vines unhealthy. Would that I were able to give the reader some encouragement as to its cause and prevention, or cure; but some of our oldest and most experienced vine-planters have come to the conclusion, as to treatment, that "the more they find out, the more they don't know." It is now generally conceded that it is caused by a fungus growth. That on the leaves is probably the _Oidium Tuckeri_, and it is generally supposed that the mildew and rot of the berries is owing to the same cause. The microscope clearly indicates its fungoid character. As to the causes, it must be admitted that the weather favors or prevents its access, and that so far it is a proximate cause, but that the spores are the true origin of the trouble. The Cincinnati Horticultural Society, whose members have long had opportunities of studying this malady, have come to the following conclusions, which, it will be seen, are not very satisfactory.

_To the Cincinnati Horticultural Society_:--We have been appointed by you to discharge a certain function. Having examined the premises and considered the subject, we do now report: That, notwithstanding the discouragements attendant upon the experience of most vine-dressers during the past season, we are determined to persevere in viticulture, for the following among other reasons:

We have our capital invested in a way which _has been_ profitable, and we believe _will be_ so again.

Our lands are occupied with a growth that has required time and labor to produce, and which we are unwilling to sacrifice.

We do not believe that the diseases to which the vines and fruit have been subjected, are dependent upon long pruning or short pruning, upon deep culture or shallow, nor any of the causes to which it has been attributed, that are under the immediate control of man, but that the cause is CLIMATIC.

We do not believe that the rot and mildew can be warded off by leaving the wood upon the vines, nor that the usual vineyard method called short pruning, will render our vineyards more subject to this disease.

We do believe, however, that we have yet much to learn in regard to the _philosophy of pruning_ which it were well for us to study, and that by so doing we may gather some useful hints in relation to this very important part of a vine-grower's duties.

We do believe, as a result of our observations, that some varieties of grapes are more healthy and vigorous than others; and, on the other hand, that some are peculiarly subject to the inroads of these maladies which have so terribly affected the fruit, the foliage, and the green wood of our vines. We do firmly believe, that our societies should avoid recommending the extensive planting of any trees or vines that have not proved themselves general healthy, and free from the maladies in question, for a number of years, after trial in different situations.

We do believe that systematic efforts should be made with different remedial and preventive agents, to avert the disasters that have overtaken our vine-crops of late years, and, with this view, as we have reason to believe that the difficulty depends upon the existence of some epiphytic plant, and as we are informed that sulphur and sulphate of iron exert an obnoxious influence upon the whole cla.s.s of fungi, we recommend our brother vine-dressers to take courage, and to make vigorous and systematic efforts to ward off the difficulty the coming season, by the regular and persevering applications of these substances to their grape vines.