318 Plant Physiology 



dant toward the middle portion of the shoot. On the 

 other hand, apples are produced on wood which is two 

 years old, and the same is true of cherries and plums. 

 The pear belongs, in general, to the apple class, but on 

 old spurs the relations may be somewhat more complex. 

 It is evident, therefore, that the pruning practices with 

 respect to any particular fruit must take into consideration 

 not merely the effects upon general growth and form of the 

 tree, but must consider also a proper regulation of the 

 buds, shoots, or branches which are to produce fruit. 



185. Persistence of the rest period in temperate 

 regions. Owing to the periodic production of the ter- 

 minal bud, the shedding of the leaves, and the passage 

 of the plant into a definite state of rest each autumn, 

 it has been more or less assumed that this period is essen- 

 tial, and that it may only with great difficulty be short- 

 ened. It has been felt, particularly, that it is extremely 

 difficult to force perennials into new growth before their 

 normal resting period is completed. Klebs has shown, 

 however, that under favorable conditions for growth, a 

 number of plants require no winter rest period, and may 

 be cultivated more or less continuously. 



More recently, Howard and others have demonstrated 

 that, even with those plants which are most persistent 

 in refusing to grow until the normal rest period is over, 

 etherization or other special forcing may be effective in 

 giving the necessary stimulus to early growth (as devel- 

 oped later, section 197). First, however, it is necessary 

 to indicate the effect of restoring, during the resting period, 

 favorable conditions for growth. It is shown that of 

 234 species of plants brought into the greenhouses at 



