REQUIREMENTS FOE LIGHT. 



31 



and moisture than on the possession of certain qualities, 

 among which is the ability to bear shade. With regard 

 to this power 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. (See figs. 27, 28.) Tolerant trees are those 

 which nourish under more or less heavy shade in early 



Fig. 28. — Heavy crowns of a tolerant species. 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. Conse- 



