REQUIREMENTS FOR LIGHT. 



31 



and moisture than on tlie possession of certain qualities, 

 among which is the ability to bear sliade. With regard 

 to this x)ower trees are roughly divided into two classes, 

 often called shade-bearing and light-demanding, follow- 

 ing the German, but better named tolerant and intoler- 

 ant of shade. (Seefigs. 27, 28.) Tolerant trees are those 

 which nourish under more or less heavy shade in early 



Fig. 28. — Heavy cruuiia ..1 a tulciaut 8i»eciL'.s. The Alpine Fir in northern 



Washington. 



youth; intolerant trees are those which demand a com- 

 paratively slight cover, or even unrestricted light. 

 Later in life all trees require much more light than at 

 first, and usually those of both classes can live to old 

 age only when they are altogether unshaded from above. 

 But there is always this difference between them : the 

 leaves of tolerant trees will bear more shade. Oonse- 



