A CO-AIMINITY OF TREES. 



45 



its leaves and twigs, and aids in keeping the air about 

 tbeir crowns, and the soil abont their roots, cooler in 

 summer and warmer in winter than it would be if each 

 tree stood alone. (See PI. XXI Y.) With the others it 

 forms a common canopy under which the seedlings of 

 all the members of this protective union are sheltered 

 in early youth, and through which the beneficent influ- 



FiG. 41. — A forest in Switzerland where the mutual help of the trees is at its 

 best. The Sihlwahl, where this picture was taken, has been well managed 

 since beiore the discovery of America, 



ence of the forest is preserved and extended iar beyond 

 the spread of the trees themselves. But while this 

 fruitful cooperation exists, there is also present, just 

 as in a village or a city, a vigorous strife for the good 

 things of life. For a tree the best of these, and often 

 the hardest to get, are water for the roots and space and 

 light for the crown. In all but very dry places there is 



