IMPROVEMENT OF PLANTS 163 



Time for Pruning. When branches are partly broken off by 

 storms or accident, they should be removed at once. Dead or 

 diseased branches should also be promptly cut off as soon as dis- 

 covered, regardless of the season. General pruning should be 

 done while the trees are in the dormant state, either in the fall 

 or spring. 



If the pruning is done in the spring, the wound heals readily, 

 but there is a waste of the plant's energy in the loss of the accu- 

 mulated food supply by the removal of the terminal portions of 

 the branches. Spring pruning lessens wood production and in- 

 duces fruitage. 



If the pruning is done in the fall, the wound does not heal readily 

 and may become diseased, but on the other hand many immature 

 branches that would be killed by hard freezing in the winter would 

 be removed and the vigor of the plant improved thereby. Late 

 fall or winter pruning always favors wood production. 



In transplanting trees, whether in the fall or early spring, it 

 is always best to prune them rather closely. A great many of 

 the roots are injured and broken in digging up the tree, and 

 pruning of the branches is absolutely necessary to equalize its 

 leaf and root surface. It will also reduce the amount of surface 

 exposed to the action of the wind so that the tree will not be 

 blown down or moved out of place. 



Variation by Cross Fertilization. Many plants produce flowers 

 which are self-fertilized, but the resulting offspring in many cases 

 is not so strong and vigorous as when the flowers are fertilized 

 by the pollen of another plant. If both plants are of the same 

 kind, the resulting offspring is called a cross; but if the plants are 

 of different kinds, as a raspberry and a blackberry, the offspring is 

 called a hybrid. Hybrids and crosses are generally different from 

 both parents, but often combine and emphasize some of the good 

 qualities of each. By repeating this process a number of times 

 with flowers of carefully selected individuals we may eventually 

 originate a new plant and make it a permanent type. In plant- 

 ing the resulting seed we frequently find that the offspring do not 

 come true to the seed and that there is a tendency to revert to 

 the original or ancestral type. Constant vigilance and enduring 

 patience alone will insure success. 



