ON PEARS. 
109 
2. It is agreeable to all that we know of the effects of freezing that the new wood, or 
the latest growth, should suffer most. Thus the young of peach trees in some locations is 
often destroyed. The ends of limbs are dead. But not so in blight. The disease rarely 
begins with the extremity, but usually in the middle of a branch, as has been already 
described, and this not until after the limb has been covered with a vigorous growth of 
leaves and new wood, or an extension of its branches has taken place. In such a case it 
can hardly be supposed that it is really the same sap which has been supposed to have 
been frozen in the opening of spring, or during the winter. This sap has already been 
expended in the growth of new parts, and a new formed sap supplies the plant with this 
circulating fluid. 
3. It seems more consonant with facts, to infer that when a vegetable is destroyed, im¬ 
mediately or ultimately, by frost, that death takes place by injury which the solids sustain, 
rather than by the injury of the fluids. The change in this case in the fluids is an effect, 
and not a cause—the solids themselves being the organs by which healthy fluids are gene¬ 
rated, though it still remains true that when the fluids are imperfectly formed, or are chan¬ 
ged in their essential properties, that death or injury to the structure must necessarily fol¬ 
low, notwithstanding the solids are in a healthy state. The foregoing considerations are 
sufficient with us for the rejection of the theory which maintains that frozen sap is proxi- 
mately the cause of blight in fruit trees. To these we might still add other considerations 
which go to disprove it. So w T e dissent, also, from the views of the author of this theory 
in regard to the proposed remedy, viz., a coating of whitewash. This seems to have been 
proposed from a misapprehension of the nature of the coating itself; for, in fact, so far as 
the coating operates at all, it must promote rather than retard the freezing of the sap. An 
earthy material, of the nature of whitewash, is a better conductor of heat than the porous 
and partially dry cuticle itself. The remedy which has been proposed for the treatment of 
blight, is simple, but strikes not at the root of the evil. The limb, when found affected, 
may be removed ; it is no longer a living part of the vegetable system. A close inspection 
of the bark, with incisions of the cuticle, will show the extent of the disease, and all that 
is diseased may be removed at once. It does not follow, however, that because a limb is 
not removed the whole tree will certainly die, for instances do occur where the tree lives 
on with its dead branches remaining. The knife, however, can be freely applied, for 
the limb is irreparably gone, and the fear that contaminated fluids may occur, by which 
the disease is extended, may stimulate us to the excision of the member. 
The period when the blight begins is about the middle of June, after there has been a 
considerable part of the growth of wood for the year. It must often seem that temperature 
has something to do with the disease, and still the only fact which favors this view of the 
subject, is time, for it is not to be supposed that a certain degree of heat will cause the dis¬ 
ease, and if it has any thing to do with it, it is only one of the conditions. Without recur¬ 
ring to theoretical grounds, or those which stand upon the known properties of matter, as 
it regards the conductibility of caloric, we believe experience has fully disproved the 
theory. 
