THE LEAVES 89 



rate, and as a consequence they wilt more or less. 

 The wiltmg is itself a protection against serious in- 

 jury, for in this condition the openings on the lower 

 surface of the leaf are closed, and the drooping posi- 

 tion assumed by the blade operates to diminish the 

 amount of water thrown off into the air. 



115. Transplanting trees and herhs is attended 

 by wilting. — A plant usually develops a system of 

 roots with hairs capable of supplying the necessary 

 amount of moisture to the leaves, and when it is 

 lifted from the ground the process is attended with 

 more or less damage to the roots or hairs. When 

 the plant is set in a new position its absorbing pow- 

 ers are not so great as before, and if it is allowed to 

 retain all of its leaves, it will throw olf more water 

 than it receives, and wilting will result. To avoid 

 this the branches are trimmed in such manner as to 

 reduce the evaporating surface to the proper propor- 

 tion to the roots. One may see nurserymen putting 

 out trees, the tops of which have been trimmed to 

 bare poles. 



116. Freezing or frosting. — An observation of 

 the plants growing in the open air after the first 

 frost of autumn will show that the leaves of some 



