106 PRINCIPLES OF PLANT CULTURE 



more mature leaves are precipitated by the first autumn 

 frost. Those less mature usually remain until the more 

 severe frosts. In trees with well-ripened wood, the leaves 

 at the tip of the shoots usually fall before, or not later 

 than, those on the older parts of the tree. With poorly- 

 matured wood the reverse is the case. In a few deciduous 

 trees, as the beech and some oaks, many of the mature 

 leaves remain on through the winter. 



174. Hardiness depends upon the degree to which the 

 dormant state is assumed. Since the most severe climatic 

 extremes come during the natural rest-period of plants, 

 the ability of the plant to endure these extremes depends 

 upon the extent to which the protoplasm becomes dormant 

 during the decline of growth. As a rule, a given plant is 

 hardy (10) in a locality in which the duration and the 

 warmth of the growing season are sufficient to complete 

 and fully mature its normal amount of growth. Varieties 

 of the apple and other trees, that so far complete their 

 growth in any given locality that their leaves fall before 

 hard frosts, are rarely injured in winter, while those that 

 continue growth until their foliage is destroyed by freezing 

 suffer in severe winters. Deciduous trees are liable to 

 destruction in severe winters in a climate where none of 

 the leaves fall before hard frosts, as is the case with the 

 peach, apricot and nectarine in northern United States. 



175. Acclimatizing. — Individual plants cannot adjust 

 themselves to a new environment, except to a slight ex- 

 tent. The power to complete the annual growth processes 

 and become sufficiently dormant to endure the rigor of 

 the rest period in any given locality is inherited, and not 

 acquired. We are, therefore, able to do very little toward 

 inuring or acclimatizing individual plants to an environ- 

 ment to which they were not adapted by nature. We 



