In an article on employing suckers of fruit-trees for stocks, which we
shall copy, Dr. Kirtland says:
“The practice of grafting and budding pears upon this
quality of stocks has extended a diseased action, a kind of
canker among our pear orchards, that has, in some instances,
been mistaken for _blight_, a disease that has its origin in
the depredations of a minute coleopterous insect, which has
been satisfactorily described in all its stages of
transformation by Dr. Harris, and other Massachusetts
entomologists.”
That the fire-blight is, to any considerable extent anywhere, but
especially at the West, occasioned by an insect, is an idea, we
believe, totally unsupported by facts. That some injury has been done
by the _scolytus pyri_, the investigations of Mr. Lowell and Professor
Peck leave no room to doubt. But we are not satisfied that, even in
these cases, they were the cause of the _blight_, but only an
accidental concomitant. Did Mr. Lowell or Professor Peck _always_ find
this beetle upon blighted trees? Was it found in _every_ blighted
limb? Did not blight occur without these insects? Has any one of New
England _since_ found the blight to proceed from the gnawings of this
beetle?
Has any one found this beetle _before_ the blight occurred at its
mischievous work, or is it only _after_ the blight is seen that the
beetle is found? If the _scolytus pyri_ has been _found_ only after
the tree is thoroughly affected, there is reason to suppose that it
did not _come_ until after the disease had prepared the way for it.
We are seriously skeptical of this alleged cause. Whatever may be true
of the blight at the East, the blight in the West is unquestionably
not an effect of the _scolytus pyri_. We have examined with the utmost
pains, multitudes of trees in all soils—several of our shrewdest
nurserymen have searched year by year, and we have, unfortunately, had
too much opportunity and too many subjects, and yet no insect or
insect-track has been detected, except those which have attacked the
tree in _consequence_ of the blight.
To be sure, we can find bugs, black, brown, green and grey, but the
mere presence of an insect is nothing, though with many, it seems
enough, when a tree is blighted, if a bug is found on it, to determine
the parentage of the mischief. Nor do the published accounts of
insects, found on blighted trees, increase our respect for this
theory. The observations seem to have been not thorough enough, and
not carefully made, and the reasonings even less philosophical. Men
have searched for a theory rather than for the mere facts in the case.
But by far the greatest number of those who write, give no evidence of
relying upon any observations which they have themselves made, but go
back perpetually to the old precedents, Mr. Lowell and Professor Peck,
without being at any pains to verify them, Has Dr. Kirtland ever found
the _scolytus pyri_? Has he ever, in time of extensive blight, found
it under such circumstances as to satisfy his mind that it was the
real cause of fire-blight? or does he rest satisfied that blight is
occasioned by an insect simply because so it is set down in good
books? The canker may be mistaken for blight by those who have not
been acquainted with either; but surely, no one who has ever
attentively examined one real case of fire-blight, would ever mistake
it for anything else, or anything else for it.
The insect theory we regard as wholly untenable except for special,
local, peculiar ravages which are not properly _blights_. The blight
is a disease of the _circulation_. It affects every tissue of the
plant. It is not a disease from exhaustion of sap by the suction of
aphides, as Dr. Mosher, of Cincinnati, supposed, for the trees have a
plethora rather than scarcity of sap; it lacerates the sap-vessels,
bursts the bark, flows down the branches, and dries in globules upon
the trunk. On cutting the tree, if the blight is yet new, the texture
of the alburnum will be found to resemble what is called a
_water-core_ in the apple, its color is of a dirty greenish hue, soon
changing by exposure to brown and black. But if the blight is old, the
wood is of a dingy white, the alburnum colored like iron rust, and the
bark of a brownish black. These appearances are incompatible with any
idea of exhaustion by the gnawing of the _scolytus pyri_, or the
suction of aphides, which would result in mere shrinking of parts,
dryness and death. If insects have a hand in the mischief, it is by
the secretion of poison, of which fact, we have never seen the trace
of proof, although it has often been suggested, and is by some
empyrically asserted. To our minds the insect-poison-theory is
imaginary. It is entirely convenient to refer every excrescence, or
shrinking of parts, every watery suffusion, wart, discoloration,
crumpling leaf, wilting, etc., to poison, and still more convenient to
find the insect so atomic that it cannot _be_ found, and thus to heap
the multiform sins of the orchard on the scape-goat of a hypothetical
insect.
As to electricity, as no one knows anything about this elemental
sprite, his out-goings or in-comings, we are like to have acted over
again all the caprices of witch-times, when elves and gnomes cut up
every prank imaginable, and when any prank, which was cut up, of
course was performed by them. Everybody is agog about electricity. But
we respectfully suggest that it is one thing to ascertain facts by
cautious, guarded experiments or careful observation, and quite
another to set down everything, which one does not know what else to
do with, to electricity, simply because _it may be so for aught that
we know to the contrary_. People reason somewhat in this wise;
electricity performs a vast number of very mysterious operations,
therefore, every operation which is mysterious is performed by
electricity. We believe electricity to have something to do with it,
only because it seems to have concern with every living, growing
thing.
We believe that the blight is, in all cases, the effect of frost upon
the sap. We have, until recently, supposed it to arise from autumnal
freezing, while the tree is in full growth. We are now inclined to
suppose that severe freezing and sudden thawing at any time, autumn,
winter or spring, _when the sap is in motion_, will result in blight.
The blight of 1844 was from the freezing of growing trees in the
autumn of 1843, and the premonitory stages were clearly discernible in
the tree during the whole winter months before it broke out in its
last malignant form.
When a warm winter allows continuous motion of sap, and sudden, severe
freezing with rapid thawing occurs, we _suppose_ it to cause a variety
of blight. We are making investigations on this head, but are not yet
prepared to speak with certainty.
When a sudden violent freezing overtakes growing trees in spring, with
rapid thaws, it, we suppose, results in a blight resembling the
autumn-caused blight.
We are diligently searching into this whole matter, and hope to throw
some light upon it.
But now comes _the_ question. What is it that makes some trees so
obnoxious to this evil while others escape? Why are some orchards
generally affected, and contiguous orchards entirely saved?
It is very plain that the blight occurs, as a general disease, in some
seasons more than in others, because it depends upon the peculiar
condition of the season, the time and degree of frosts. But it does
not seem so clear why, when these conditions are favorable to blight,
one tree should suffer, and the next in the row should not; why one
orchard should be depopulated, and another in the same town not
touched.
We think that light will be afforded on this point by a consideration
of the _texture_ of trees.
When trees are rapidly grown by stimulating manures, or upon strong
clay loams, or from any other cause, the wood is coarse, the passages
enlarged, the tissue loose and spongy. The tree passes a great volume
of sap—it is but imperfectly elaborated (as is seen by the late period
to which such trees defer the bearing of fruit), and the tissues
formed by it are correspondingly imperfect in wholesomeness,
compactness, and solidity of parts. The tree is bloated—is dropsical.
On gravelly soils, or loams with a gravelly subsoil, or on any kind of
soil, which gives a slow and thorough growth, the wood is fine, close
and perfect; the vessels are not expanded, their sides are firmer,
less sensitive to sudden changes of temperature, and when exposed to
them better able to resist them.
Whatever soil produces rank or coarse wood, a flabby tissue will be
subject to blights. Whatever soil induces a fine-grained, compact
fibre, and vigorous tissue, will be free from blight. The same is true
of the various methods of cultivation; those who drive their trees,
who aim chiefly at a rapid and strong growth, will give their trees a
condition requisite for blight. Those who pursue a more cautious, a
slower method, and look to the _quality_ rather than the _quantity_ of
their wood, will be comparatively free from blight.
To be sure, there may be seasons so extreme that blight will occur in
the most healthy tree; so disease will occur in the most temperate
men; yet temperance, conformity to the laws of nature, is the rule of
health, and nonconformity the preparation for disease.
Meanwhile, will those who are unfortunate enough to have a good
opportunity for observing, examine—