Chapter III: CAUSE OF THE BLIGHT.—The Indiana Horticultural Society, early in

the summer of 1844, appointed a committee to collect and investigate facts on the Fire-Blight. While serving on this committee, and inquiring in all the pear-growing regions, we learned that Reuben Reagan, of Putnam County, Ind., was in possession of much information, and supposed himself to have discovered the cause of this evil; and to him we are indebted for a first suggestion of the cause. Mr. Reagan has for more than twelve years past suspected that this disease originated in the fall previous to the summer on which it declares itself. During the last winter Mr. Reagan predicted the blight, and in his pear-orchards he marked the trees that would suffer, and pointed to the spot which would be the seat of the disease; and his prognostications were strictly verified. After gathering from him all the information which a limited time would allow, we obtained from Aaron Alldredge, of Indianapolis, a nurseryman of great skill, and possessed of careful, cautious habits of observation, much corroborative information; and particularly a tabular account of the blight for nine years past in his nursery and orchard.

The spring of 1843 opened early, but cold and wet, until the last of May. The summer was both dry and cool, and trees made very little growth of new wood. Toward autumn, however, the drought ceased, copious rains saturated the ground, and warm weather started all trees into vigorous, though late, growth. At this time, while we hoped for a long fall and a late winter, on the contrary we were surprised by an early and sudden winter, and with unusual severity at the very beginning. In the West, much corn was ruined and more damaged; and hundreds of bushels of apples were caught on the trees and spoiled—one cultivator alone losing five hundred bushels. Caught in this early winter, what was the condition of fruit-trees? They were making rapid growth, every part in a state of excitement, the wood unripe, the passages of ascent and descent impleted with sap. In this condition, the fluids were suddenly frozen—the growth instantly checked; and the whole tree, from a state of great excitability, was, by one shock, rudely forced into a state of rest. Warm suns, for a time, followed severe nights. What would be the effect of this freezing and sudden thawing upon the fluids and their vessels? We have been able to find so little written upon vegetable morbid anatomy (probably from the want of access to books), that we can give but an imperfect account of the derangement produced upon the circulating fluids by congelation. We cannot state the specific changes produced by cold upon the ascending sap, or on the cambium, nor upon the elaborated descending current. There is reason to suppose that the two latter only suffer, and probably only the last. That freezing and thawing decompose the coloring matter of plants is known; but what other decomposition, if any, is effected, we know not. The effect of congelation upon the descending sap of pear and apple-trees, is to turn it to a viscid, unctuous state. It assumes a reddish brown color; becomes black by exposure to the air; is poisonous to vegetables even when applied upon the leaf. Whether in some measure this follows all degrees of congelation, or only under certain conditions, we have no means of knowing.

The effect of freezing and thawing upon the tissues and sap-vessels is better known. Congelation is accompanied with expansion; the tender vessels are either burst or lacerated; the excitability of the parts is impaired or destroyed; the air is expelled from the aëriferous cavities, and forced into the passages for fluids; and lastly, the tubes for the conveyance of fluids are obstructing by a thickening of their sides.[19] The fruit-trees, in the fall of 1843, were then brought into a morbid state—the sap thickened and diseased; the passages lacerated, obstructed, and probably, in many instances burst. The sap elaborated, and now passing down in an injured state, would descend slowly, by reason of its inspissation, the torpidity of the parts, and the injured condition of the vessels. The grosser parts, naturally the most sluggish, would tend to lodge and gradually collect at the junction of fruit-spurs, the forks of branches, or wherever the condition of the sap-vessels favored a lodgment. In some cases the passages are wholly obstructed; in others, only in part.

At length the spring approaches. In early pruning, the cultivator will find, in those trees which will ere long develop blight, that the knife is followed by an unctuous sap, and that the liber is of a greenish yellow color. These will be the first signs, and the practised eye may detect them long before a leaf is put forth.

When the season is advanced sufficiently to excite the tree to action, the sap will, as usual, ascend by the alburnum, which has probably been but little injured; the leaf puts out, and no outward sign of disease appears; nor will it appear until the leaf prepares the downward current. May, June and July, are the months when the growth is most rapid, and when the tree requires the most elaborate sap; and in these months the blight is fully developed. When the descending fluid reaches the point where, in the previous fall, a total obstruction had taken place, it is as effectually stopped as if the branch were girdled. For the sap which had lodged there would, by the winds and sun, be entirely dried. This would not be the case if the sap was good and the vitality of the wood unimpaired; but where the sap and vessels are both diseased, the sun affects the branch on the tree just as it would if severed and lying on the ground. There will, therefore, be found on the tree, branches with spots where the bark is dead and shrunk away below the level of the surrounding bark; and at these points the current downward is wholly stopped. Only the _outward_ part, however, is dead, while the _alburnum_, or sap-wood, is but partially injured. Through the alburnum, then, the sap from the roots passes up, enters the leaf, and men are astonished to see a branch, seemingly dead in the middle, growing thriftily at its extremity. No insect-theory can account for this case; yet it is perfectly plain and simple when we consider that there are two currents of sap, one of which may be destroyed, and the other for a _limited time_ go on. The blight, under this aspect, is nothing but _ringing_ or _decortication_, effected by diseased sap, destroying the parts in which it lodges, and then itself drying up. The branch will grow, fruit will set, and frequently become larger and finer flavored than usual.

But in a second class of cases, the downward current comes to a point where the diseased sap had effected only a partial lodgment. The vitality of the neighboring parts was preserved, and the diseased fluids have been undried by wind or sun, and remain more or less inspissated. The descending current meets and takes up more or less of this diseased matter, according to the particular condition of the sap. Wherever the elaborated sap passes, after touching this diseased region, it will carry its poison along with it down the trunk, and, by the lateral vessels, in toward the pith. We may suppose that a violence which would destroy the health of the outer parts, would, to some degree, rupture the inner sap-vessels. By this, or by some unknown way, the diseased sap is taken into the inner,[20] upward current, and goes into the general circulation. If it be in a diluted state, or in small quantities, languor and decline will be the result; if in large quantities, and concentrated, the branch will die suddenly, and the odor of it will be that of frost-bitten vegetation. All the different degrees of mortality result from the quantity and quality of the diseased sap which is taken into circulation. In conclusion, then, where, in one class of cases, the feculent matter was, in the fall, so virulent as to destroy the parts where it lodged, and was then dried by exposure to wind and sun, the branch above will live, even through the summer, but perish the next winter; and the spring afterward, standing bare amid green branches, the cultivator may suppose the branch to have blighted that spring, although the cause of death was seated eighteen months before. When, in the other class of cases, the diseased sap is less virulent in the fall, but probably growing worse through the spring, a worse blight ensues, and a more sudden mortality.

We will mention some proofs of the truth of this explanation.

1. The two great blight years throughout the region of Indianapolis, 1832 and 1844, were preceded by a summer and fall such as we have described. In the autumns of both 1831 and 1843, the orchards were overtaken by a sudden freeze while in a fresh-growing state; and in both cases the consequence was excessive destruction the ensuing spring and summer.

2. In consequence of this diagnosis, it has been found practicable to predict the blight six months before its development. The statement of this fact, on paper, may seem a small measure of proof; but it would weigh much with any candid man to be told, by an experienced nurseryman, this is such a fall as will make blight; to be taken, during the winter into the orchard, and told, this tree has been struck at the junction of these branches; that tree is not at all affected; this tree will die entirely the next season; this tree will go first on this side, etc., and to find, afterward, the prediction verified.

3. This leads us to state separately, the fact, that, after such a fall, blighted-trees may be ascertained during the process of late winter or early spring pruning.

In priming before the sap begins to rise freely, no sap should follow the knife in a healthy tree. But in trees which have been affected with blight, a sticky, viscid sap exudes from the wound.

4. Trees which ripen their wood and leaves early, are seldom affected. This ought to elicit careful observation; for, if found true, it will be an important element in determining the value of varieties of the pear in the middle and western States, where the late and warm autumns render orchards more liable to winter blight than New England orchards. An Orange Bergamot, grafted upon an apple stock, had about run out; it made a small and feeble growth, and cast its leaves in the summer of 1843, long before frost. It escaped the blight entirely; while young trees, and of the same kind (we believe), standing about it, and growing vigorously till the freeze, perished the next season. I have before me a list of more than fifty varieties, growing in the orchard of Aaron Alldredge, of Indianapolis, and their history since 1836; and so far as it can be ascertained, late-growing varieties are the ones, in every case, subject to blight; and of those which have always escaped, the most part are known to ripen leaf and wood early.

5. Wherever artificial causes have either _produced_ or _prevented_ a growth so late as to be overtaken by a freeze, blight has, respectively, been _felt_ or _avoided_. Out of 200 pear-trees, only four escaped in 1832, in the orchard of Mr. Reagan. These four had, the previous spring, been _transplanted_, and had made little or no growth during summer or fall. If, however, they had recovered themselves, during the summer, so as to grow in the autumn, transplanting would have had just the other effect; as was the case in a row of pear-trees, transplanted by Mr. Alldredge in 1843. They stood still through the summer and made growth in the fall—were frozen—and in 1844 manifested severe blight. Mr. Alldredge’s orchard affords another instructive fact. Having a row of the St. Michael pear (of which any cultivator might have been proud), standing close by his stable, he was accustomed, in the summer of 1843, to throw out, now and then, manure about them, to force their growth. Under this stimulus they were making excessive growth when winter-struck. Of all his orchard, they suffered, the ensuing summer, the most severely. Of twenty-two trees _twelve_ were affected by the blight, and _eight_ entirely killed. Of seventeen trees of the Bell pear, eleven suffered, but none were killed. All in this region know the vigorous habit of this tree. Of eight Crassane Bergamot (a late grower), five were affected and two killed. In an orchard of 325 trees of 79 varieties, one in seven blighted, 25 were totally destroyed. Although a minute observation was not made on each tree, yet, as a general fact, those which suffered were trees of a full habit and of a late growth.

6. Mr. White, a nurseryman near Mooresville, Morgan County, Indiana, in an orchard of from 150 to 200 trees, had not a single case of the blight in the year 1844, though all around him its ravages were felt. What were the facts in this case? His orchard is planted on a mound-like piece of ground; is high, of a sandy, gravelly soil: earlier by a week than nursery soils in this county; and in the summer of 1843 his trees grew through the summer; wound up and shed their leaves early in the fall, and during the warm spell made no _second growth_. The orchard, then, that escaped, was one on such a soil as insured an _early_ growth, so that the winter fell upon ripened wood.

7. It may be objected, that if the blight _began_ in the new and growing wood, it would appear there; whereas the seat of the evil, _i. e._ the place where the bark is diseased or dead, is lower down and on old wood. Certainly, it should be; for the returning sap falls some ways down before it effects a lodgment.

8. It might be said that _spring-frosts_ might produce this disease. But in the spring of 1834, in the last of May, after the forest-trees were in full leaf; there came frost so severe as to cut every leaf; and to this day the dead tops of the beech attest the power of the frost. But no _blight_ occurred that year in orchard, garden or nursery.

9. It may be asked why forest-trees do not suffer. To some extent they do. But usually the dense shade preserves the moisture of the soil, and favors an equal growth during the spring and summer; so that the excitability of the tree is spent before autumn, and it is going to rest when frost strikes it.

10. It may be inquired why fall-growing shrubs are not always blighted, since many kinds are invariably caught by the frost in a growing state.

We reply, first, that we are not to say that _every_ tree or shrub suffers from cold in the same manner. We assert it of fruit-trees because it has been observed; it must be asserted of other trees only when ascertained.

We reply more particularly, that a _mere frost_ is not supposed to do the injury. The conditions under which blight is supposed to originate are, a growing state of the tree, a sudden _freeze_, and sudden thawing.

We would here add, that many things are yet to be ascertained before this theory can be considered as settled; as the actual state of the sap after congelation, ascertained by experiment; the condition of sap-vessels, as ascertained by dissection; whether the congelation, or the thawing, or both, produce the mischief; whether the character of the season _following_ the fall-injury may not materially modify the malignancy of the disease; seasons that are hot, moist and cloudy, propagating the evil; and others dry, and cool, restraining growth and the dsease. It is to be hoped that these points will be carefully investigated, not by conjecture, but by scientific processes.

11. We have heard it objected, that trees grafted in the spring blight in the graft during the summer. If the _stock_ had been affected in the fall, blight would arise from _it_; if the scion had, in common with the tree from which it was cut, been injured, blight must arise from _it_.

Blight is frequently caused in the nursery; and the cultivator, who has brought trees from a distance, and with much expense, has scarcely planted them before they show blight and die.

12. It is objected, that while only a single branch is at first affected, the evil is imparted to the whole tree; not only to the wood of the last year, but to the old branches. We reply, that if a single branch only should be affected by fall-frost, and be so severely affected as to become a repository of much malignant fluid, it might gradually enter the system of the whole tree, through the circulation. This fact shows, why _cutting_ is a partial remedy; every diseased branch removed, removes so much poison; it shows also why cutting from _below_ the seat of the disease (as if to fall below the haunt of a supposed insect), is beneficial. The farther the cut is made from that point where the sap has clogged the passages, the less of it will remain to enter the circulation.

13. Trees of great vigor of constitution, in whose system but little poison exists, may succeed after a while in rejecting the evil, and recover. Where much enters the system, the tree must die; and with a suddenness proportioned to the amount of poison circulated.

14. A rich and _dry_ soil would be likely to promote early growth, and the tree would finish its work in time; but a rich and _moist_ soil, by forcing the growth, would prepare the tree for blight; so that rich soils may prevent or prepare for the blight, and the difference will be the difference of the respective soils in producing an early instead of a late growth.