THE WOBK OF STEMS 261 



bulbs, corms, etc., are usually protected by the dead 

 leaves of the previous season which enwrap them. 



The beautiful arrangements of leaves whereby they 

 spread out over a great area so as to absorb sunshine 

 without mutual interference would not be possible 

 without a proper grouping of the branches on which 

 they are borne. How do the stems aid the leaves in 

 securing the best arrangement ? What do you think is 

 the most advantageous arrangement of the branches 

 (and of the leaves upon them), in order that the 

 greatest amount of sunshine may be absorbed with the 

 greatest economy of material? Take into considera- 

 tion the daily motion of the sun. Notice the difference 

 between a tree growing in the woods and one growling 

 in the open, where it receives light from all sides. As 

 soon as we begin to study the forest- grown tree we 

 notice that the lower part of the trunk appears free 

 from limbs, not because none have appeared in that 

 region but simply because they have perished from 

 lack of light. This process is called self- pruning, and 

 to it is due the value of the tree for lumber, since it 

 results in straight timber free from knots. In the tree 

 grown in the open self- pruning also occurs, though to 

 a much smaller extent. 



There is a continual struggle going on among the 

 branches for light and space, which results in stunting 

 and dwarfing the weaker ones or in killing them alto- 

 gether. Many factors afEect the result; the position 



