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It is quite universally accepted that the best time to cut hard- 

 woods is in the winter. Wood so cut is believed to season better, to 

 be more durable, and in every way more desirable where exacting 

 service is demanded. Scientific investigations have demonstrated 

 that there are at least partial grounds for such claims. It is when 

 explanation is made that science and popular belief are no longer 

 in harmony. 



The popular notion is that during the winter the sap of a hard- 

 wood tree is down — probably in the roots. On this account the 

 trunk and branches of a tree contain considerably less moisture in 

 winter than spring and summer. Accordingly, wood cut "when the 

 sap is down" will be comparatively dry to start with, and having 

 reached this condition in the living tree much of the damage of 

 seasoning in open air is avoided. Moreover, according to this 

 theory, since it is fermentation of the sap which causes wood to 

 rot, of course the best time to cut timber is when there is the least 

 sap; that is, when the "sap is down." 



The trouble with these plausible theories is that they are based 

 on false premises. In the first place there is more sap in a living 

 tree in winter than in summer, and secondly, decay is not due to 

 sap fermentation, but to the action of living organisms of which 

 fungi are by far the most important. 



It is easy to understand how the erroneous idea of the movement 

 of sap was gained. In the early spring some trees, like the maple, 

 bleed very freely when cut or tapped. Later, when the foliage is 

 young, there is a mucilaginous layer just under the bark, and it is 

 so soft and slippery that bark can be peeled off very readily at 

 that season. This fact is taken advantage of in peeling logs, posts, 

 poles and harvesting tanbark. The time to make a pawpaw whistle 

 is, as everyone knows, "when the sap is up." If the sap goes up 

 in the spring, as seems quite evident, what is more natural than 

 that it should go down in the fall and stay down all winter? 



To understand the movement of sap, it is first necessary to know 

 what sap is and where it comes from. Tree sap is water containing 

 various substances in solution. The water is absorbed from the 

 soil by the roots and makes its way upward through the sapwood 

 of the tree to the leaves. It contains small quantities of mineral 

 salts and in some species, as birch, maple and walnut, it also con- 

 tains at certain times a small percentage of sugar and other organic 

 matter. No satisfactorj- explanation can be made as to the real 

 cause or causes of the rise of sap. The fact remains that water 

 with small amounts of mineral salts in solution is taken in by the 

 roots and passes upward through the vessels in the sapwood of hard- 

 woods (through the tracheids of conifers) to the leaves, where most 

 of it is breathed (transpired) out into the air. The mineral salts 

 are left behind in the wood and leaves, and make up the ash when 

 the materia] is burned. 



But trees cannot live by water and mineral salts alone. Such 

 materials are in nowise fitted to enter directly into the process of 

 cell formation. Every plant needs starch. The machinery for mak- 

 ing it is supplied by the green chlorophyll of the leaves, the energy 

 by direct sunlight, and the raw materials are carbon dioxide from 

 the air and hydrogen from the water the roots absorbed. In taking 

 the hydrogen from the water (which is a compound of hydrogen 

 and oxygen), oxygen is liberated. If one examines plants in an 

 aquarium on a bright day it will be noticed that they are giving off 

 little bubbles. These are of oxygen and serve to keep the water 

 in condition for fish which breathe out carbon dioxide the plant 

 needs, and inhale the oxygen the plant gives off. At night plants 

 cannot make starch, since the power (sunlight) is shut off. 



During the day each little grain of chlorophyll has been busy 

 piling up starch all about it. During the night this material is 

 converted into sugar which is soluble and carried away to the 

 growing parts of the plant that need it. This is why plants grow 

 more on warm nights than on warm days. The day is largely de- 

 voted to making food, the night to making tissue out of the food. 



—22— 



From the above, two things are evident. First, that there must 

 be a continual movement of sap down as well as up, and second, 

 that the sap. containing the manufactured food is quite different 

 in its consistency from that taken in by the roots. The two streams 

 flow in different channels. That containing the elaborated food 

 moves through the inner bark instead of through the wood. It is 

 principally a downward flow, but may be in any direction as the 

 demands of the different parts of the plant require. 



Since the living wood cells need food the same as the other parts, 

 some arrangement must be made for transferring the food sap from 

 the bark. This is accomplished by means of the medullary rays 

 which extend from the wood into the bark. These rays do more 

 than transfer food; they store some of it over winter to be used 

 in the spring before the leaves are out. This stored food is not in 

 the soluble form of sugar, but in the insoluble form of starch. 

 AVhen there is need for supplies from these storehouses the starch 

 is again converted into sugar which is dissolved in the sap of the 

 sapwood. It is for this reason that the sap of the maple is so 

 sweet in the early spring before the leaves open but not at other 

 times. 



From the foregoing it is evident that, so long as the leaves on a 

 tree are active there must be a continuous movement of sap — quite 

 rapidly upward through the wood and more slowly downward and 

 otherwise through the inner bark and the rays. In the summer a 

 tree is normally at its greatest activity, the absorption of water 

 is most rapid and the giving off (or transpiration, as it is called) 

 from the leaves is in proportion. A greater volume of water passes 

 through the tree at this season, but less stays there. The greater the 

 leaf surface exposed the greater the amount of water transpired. 

 A thrifty maple fifteen inches in diameter and fifty feet high has 

 been found to have a third of an acre of leaf surface. If the supply 

 of moisture in the soil gets too low to supply the leaves they wilt. 

 In some species the .water content of a tree can be materially re- 

 duced by girdling or by allowing the leaves to dry on the peeled 

 trees. 



During the winter practically no transpiration occurs in deciduous 

 trees, for there are no leaves. The roots, however, do not cease 

 their activity, but continue to grow slowly and absorb water even 

 in decidedly cold weather. With no chance to escape through the 

 leaves, this water or sap accumulates so that, instead of there being 

 less in a tree during winter than summer, there is appreciably more. 

 The water content of trees is greatest in the spring just before the 

 opening of the leaves. This is more noticeable in sapwood, of 

 course, than in heartwood, as the latter is dead and no longer active 

 in the transfer of sap. It does, however, respond in some degree 

 to changes in the water content of sapwood. 



Experiments made by the Vermont Agricultural Experiment Sta- 

 tion showed the water content of sugar maples in summer to be' 

 between 26 and 27 per cent; in December it was 31.5 per cent; by 

 the middle of March it was .36.-5 per cent. The results of numerous 

 experiments by the United States Forest Service indicate the same 

 thing. For instance, the average weight of lodgepole pine ties of 

 the same size cut at Bozeman, Mont., in .lune, 1902, was 157 

 pounds; in .July. 144 pounds; in August, 150 pounds; in September, 

 157 pounds; in October, 164 pounds. Winter-cut chestnut poles cut 

 at Dover, N. J., weighed more per cubic foot when green than other 

 seasons' cuts. At Pisgah, N. C, 600 chestnut poles were weighed 

 and the winter-cut was found to be considerably heavier than that 

 cut at any other season, and, except in a single case, at no time did' 

 it reach the dryness of the other cuts. 



Dr. Robert Hartig, a German investigator, made a careful study 

 of thirty different species of trees practically all of the same age 

 (sixteen years), which he grouped into three classes. He found, by 

 eliminating as far as possible all variables other than the one under 

 investigation, that the percentage of moisture contained in green 

 wood varied materially with the season, as is shown in the following 

 table: 



