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.