TREES AND THEIR METHODS 97 



sign are much like the Eiffel Tower or certain 

 types of bridge piers. The ordinary tree has a 

 much finer problem of balance and adjustment on 

 its hands. Exposed specimens have powerful re- 

 inforcement in the shape of large wind-struts near 

 the base which extend to anchoring roots much like 

 the flying buttresses of Gothic architecture. Liv- 

 ing cells are the trees' building material. Those 

 near the base must have a compressive strength 

 equal to the entire weight above. Those in a limb 

 must have strength to resist the bending power of 

 gravity. 



Trees in the forest are always very quick to take 

 advantage of every scrap of air and sunlight to 

 be had. When a citizen of a tree city falls, his sur- 

 rounding neighbours at once send out branches to 

 fill the space which he leaves vacant. The pines 

 have a habit of dropping needles around their bases 

 until they have built miniature hills on which they 

 stand. These mounds serve a very useful purpose 

 in draining the water away from their trunks. The 

 pines are exclusive almost to the point of snobbery. 

 They often mat over large areas in their vicinity 

 with their needles to such a depth that nothing else 

 can grow there. 



The manifold shapes and forms of the different 

 tree leaves often have a utilitarian basis. The im- 



