THE WORK OF STEMS 263 



oxygen is consumed. The growth of the callus and of 

 the new roots also requires a considerable amount 

 of air., 



If there are leaves on the cutting they should be 

 removed partially or entirely, to diminish the loss of 

 water, since there are no roots to keep up the supply. 

 Shading the cuttings and keeping the air moist assist 

 greatly in this respect. 1 



In many cases we find new branches springing 

 directly from the cut surface of a limb or a stump. If 

 we examine closely we find that these come, not from 

 latent buds, but from buds newly formed, as it were 

 for the emergency, by a tissue which grows out from 

 the cambium. This tissue, called the callus, will in 

 time, if left undisturbed, cover over the cut surface 

 entirely. This is of the utmost advantage to the tree, 

 since it prevents the entrance of water, fungi and 

 other ' agents of decay. If, however, the cut surface 

 is large, it should always be painted over, to preserve 

 it until the comparatively slow growth of the callus 

 covers it. (It may also be remarked that a branch 

 should always be cut off close to the tree and not at 

 a distance from it.) Pruning is the method by which 

 man regulates the struggle among the branches for 

 his own ends, and is a study by itself; to prune 

 properly requires a careful study both of the indi- 

 vidual plant and its surroundings. Pruning is a fasci- 



!See Hunn and Bailey: "The Practical Garden Book," p. 84. 



