Page:Popular Science Monthly Volume 79.djvu/455

Rh cross-sections are subject to constant specific stresses, are geometrically defined by cubic parabolas. This form results from the law of stresses under the given conditions, and may be seen in the contour of heavily supporting bridge piers, the Eiffel tower in Paris and numerous other structures. Precisely the same problem nature has solved in building the trunks of tall trees. The famous coniferous trees of California (Fig. 1) offer the best illustration for this principle. The reason for this lies in the fact that the maximum strength of the material used in one and the same engineering structure, or in a tree, being a known constant, it is evidently of the greatest economic advantage to make the specific stresses throughout as uniform as possible.

To resist great lateral bending forces, or moments caused by strong and irregular winds, the large trees of the forest are equipped with powerful wind-struts near the base and extending to the anchoring roots (Pigs. 2 and 3). The same thing the architect does when he provides for buttresses in Gothic buildings, or when he reinforces the base of a column to secure lateral stability. The more the trees are exposed to the winds, the larger the crown, the more the principle of buttresses and pillars assumes its functions. Wherever winds from a certain direction prevail, one notices plainly that in such a region the wind-struts of the trees on the side opposite to the attack of the wind are most strongly developed. In mountainous regions where on account of the rough character of the surface, the winds are very turbulent and are making their attacks in violent gusts from all directions, one may observe wonderful and grotesque shapes of root-stocks. In a seemingly almost impossible manner the roots crawl over each other, over rocks