Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] 114 BOTANY four tubes of different inside diameter, the fluid will be found to rise very much higher in the tubes having a smaller diameter. This is caused by cap- illarity or capillary attraction. When we consider that the tubes of the fibro- vascular bundles are very much smaller than any we can make out of glass, it can be seen that water might rise in the stem to some height in tubes of microscopic diameter. Another suggested me
Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] 114 BOTANY four tubes of different inside diameter, the fluid will be found to rise very much higher in the tubes having a smaller diameter. This is caused by cap- illarity or capillary attraction. When we consider that the tubes of the fibro- vascular bundles are very much smaller than any we can make out of glass, it can be seen that water might rise in the stem to some height in tubes of microscopic diameter. Another suggested method for the rise of water is given in the fact that air is found in some of the tubes in the form of bubbles, and these minute bubbles may help in the ascent of water. The greatest factor, however, is one which will be more fully explained when we study the work of the leaf. Leaves pass off an immense quan- tity of water by evaporating it in the form of vapor. This evaporation seems to result in a kind of suc- tion on the col- umn of water in the stem. In the fall, after the leaves have gone, much less water is taken in by roots, show- ing that an inti- mate relation exists between the leaves and the root. Structure of Wood.— Quite a differ- ence in color and structure is often seen between the heart wood, composed of the dead walls of cells occupying the central part of the tree trunk, and the sap wood, the living part of the stem. In trees which are cut down for use as lumber and in the manufacture of various furniture, the markings and differences in color are not always easy to understand. Cross section through a black oak showing heart wood and sap wood and medullary rays. (From Pinchot, Dept. of Agr.)
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