CHANGES ACCOMPANYING BREAKING OF REST PERIOD 53 



in the growing season. Also assimulation takes place first or at least 

 most rapidly, in those parts that first approach a state of maturity. 

 With a decreased water supply and a greatly increased deposition 

 or accumulation of carbohydrates, enzyme activity is soon checked 

 if not almost entirely inhibited. 



As the season advances, two factors act together to compel the 

 main branches to cease making length growth and form terminal 

 buds. One of these forces is the rapid accumulation of carbo- 

 hydrates in branch after branch, and the other is the approach of 

 cold weather. Here it may be objected that oak, apple, peach and 

 similar trees growing in a warm greenhouse go dormant as usual. 

 True, but growth continues much longer than on outside trees 

 because only one force is being exerted to bring about a state of 

 dormancy. In the mild climate of Central California and even in 

 sub-tropical regions as far southward as deciduous trees occur, the 

 latter behave as tho they were growing under glass. 



Deciduous trees perhaps enter their most profound state of rest 

 at about the time the leaves fall or, under glass, at the time when all 

 terminal buds have formed. That the main dormant period 

 happens to be coincident with the winter season is doubtless a mere 

 coincidence as the winter per se may, and probably does, have 

 nothing to do with the beginning of the rest. In the somewhat 

 limited observations of the writer in sub-tropical parti of America 

 and the Mediterranean countries, away from the disturbing factor 

 of frost occurrence, deciduous plants were found to conform in the 

 main to the principles of growth and dormancy as mentioned above. 

 Indeed, the same principles of growth and dormancy may be ex- 

 tended to cover deciduous plants in the tropics, where, we are told 

 by responsible observers, there may be several periods of growth 

 and repose, the cessation of growth always being followed by leaf-fall. 



During the period of the main or middle rest of trees all activity 

 does not cease by any means. The enzymes doubtless continue to 

 work and some of the products of their activity are utilized in the 

 processes of respiration. In this way the excess supply of carbo- 

 hydrates may be reduced. This is perhaps the explanation for the 

 removal of the so-called "hindrance" to growth in dormant plants 

 by means of treatments which break the rest period. The treat- 

 ments in such cases merely hasten the processes perfectly normal in 

 themselves which would take place later if the enzymes were al- 

 lowed to act in a natural manner. 



The rest period of plants does not end suddenly. On the 

 contrary, under natural conditions it ends very slowly. The tran- 



