114 Principles of Plant Culture. 



the 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. Ha-rdiness 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 ex- 

 tremes depends upon the extent to which the proto- 

 plasm 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 suf- 

 fer 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. Individual Plants Cannot Adjust Themselves to 

 a New Environment, except to a slight extent. The 

 power to complete the annual growth processes and be- 



