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*Moisture less after thaw, thus contradicting the rule.
4.5715 .1185 .0198 .43
.2003 .1002 .96
"In observing trees in continuous severe winter weather, my attention has often been called to the fact that the twigs seem somewhat duller and more somber than usual, and in some cases tend to shrivel up and have the appearance of drying out. When a warm spell comes, this condition changes, and the twigs become brighter and seem to freshen up, and sometimes I imagine that they become more plump. The freshening-up feature is especially noticeable on large clumps or groves of willow; the twigs usually take on a much brighter color during warm spells in winter than during the continued freezing weather. During thawing weather, the equilibrium is maintained between the moisture or sap in the tree top and that taken in by the roots, and as fast as moisture evaporates from the tree top, sap flows up from the roots and the equilibrium is re-established. freezing weather, the moisture, even though frozen, is probably evaporating from the tree tops; and the sap, being frozen, does not flow up from the roots and replace the evaporated moisture. Thus the equilibrium between the tree tops and roots is unbalanced, and it is at this time that the twigs become shriveled by reason of moisture being lost and not replaced.
"In support of these statements, I made the following investigation: After several days of continuous freezing weather, and at a time when I expected a thaw, I cut twigs of a variety of trees. and estimated the percentage of moisture contained in them. Again, just as soon as a thaw came, I cut
Amount of Moisture Lost in Winter.
twigs from the same trees and from the same parts of the trees, and estimated the percentage of moisture again, the object being to determine if the twigs contained less moisture after several days of continued freezing than they did a short time later, during a thaw. The last two columns of figures in the table (pages 14 and 15) are upon this subject. The average water content of those twigs cut during a freeze was 47.27 per cent, while that of those cut later, during a thaw, was 48.40 per cent, being an increase of 1.13 per cent, even though the trees had been constantly losing moisture by evaporation. Therefore I conclude that during every thaw in winter, the tree top fills with sap, and then if a sudden severe freeze comes, we are likely to have injured trees, due, no doubt, to the sudden freezing of the sap, and to the loss of moisture when none can be supplied.
"It will be interesting to calculate what weight of moisture a tree may lose in winter. A certain soft maple, standing 30 to 35 feet high, with a trunk of 15 to 18 inches in diameter near the ground, exposes from 750 to 800 square feet of surface, and loses daily by evaporation from 170 to 180 grams of moisture. A given elm tree, 12 to 15 inches in diameter at the base, possesses some 300 to 400 square feet of surface, and loses daily from 70 to 100 grams of moisture. An apple tree 30 years old, with a trunk 15 inches in diameter, with a dense, bushy top, possesses approximately from 800 to 1,000 square feet of surface, and loses daily from 275 to
350 grams of moisture." These calculations, therefore, may explain some of the injuries which follow very dry winters.
Since evaporation takes place through the bark of winter twigs, it is reasonable to suppose that the tenderness of some trees in dry winter climates (as in our plains regions) may be due to such an anatomical structure of the bark as does not resist evaporation, and that, on the other hand, hardiness may sometimes be a matter of thickness or denseness of bark. Studies in this direction have been made at Cornell, and they indicate that this supposition may be well founded in certain cases, but the investigations are not yet sufficiently extended to allow of any definite statements.
The soil determinant.-There are special adaptations of fruits to soils. Pomologists are well aware of this fact as a general truth, but very little close attention has been given, in this country, to the minor applications of it. To be explicit, it is well understood that pears flourish best on clay soils and peaches best on sandy soils, but there are, no doubt, distinct preferences amongst the varieties of pears and peaches themselves. It is possible, in fact, that each distinct family or type of varieties of any species has preferences of land and location, and it will be the business of coming generations to determine what these peculiarities are. With the increasing refinements and competitions of the future, the special and local problems must receive more and more attention. If these positions are well taken, it