52 MISSOURI AGR. EXP. STA. RESEARCH BULLETIN NO. 21 



ether treatment hindered or counteracted, to some extent, the de- 

 structive processes which were produced by freezing. 



The influence of various agents in breaking the rest period of 

 plants was studied in connection with all of the leading treatments 

 and the results were similar to those obtained by other investigators 

 It was found during the very early part of the dormant season the 

 rest period was not so easily broken as later. Also toward the close 

 of the dormant season it was difficult to induce any marked accel- 

 eration of growth. Heavy dosage of a given agent readily producing 

 growth in twigs during December or early January, was found to 

 injure the buds when treatments were made later in the season. 



A few new methods for breaking the rest period were success- 

 ful. These were immersion in weak solutions of copper sulphate, 

 hydrochloric acid, oxalic acid, acetic acid, sodium nitrate, potassium 

 chloride, and manganese dioxide. 



Conclusions. The results of the respiration studies and other 

 tests seem to justify the conclusion that the specific effect of all rest 

 period breaking agents on dormant woody tissue is the stimulation 

 of the enzymes. The experimental evidence submitted shows that 

 diastatic, proteolytic, fat-splitting and oxidizing enzymes are induced 

 to become active or, are stimulated into greater activity, by treat- 

 ing twigs with ether and other agents. The extent to which enzyme 

 stimulation will result in quick growth in dormant plants will depend 

 upon the species of plant, kind of treatment, dosage, stage of dor- 

 mancy and other factors. 



It now becomes possible to advance a theory as to the cause ot 

 the beginning as well as the end of the rest period, in woody plants. 

 In general it would seem that the rest sets in on account of the inhi- 

 bition of enzyme activity due to over-accumulation of the products 

 of their work. The early phases of the rest period occur and are 

 passed thru while the plants are in full leaf and often while some of 

 the parts are making active growth. The parts to enter the resting 

 state first in fruit trees particularly, are the so-called spurs short 

 lateral out-growths usually from wood that grew the previous 

 year. These cease growing early in the season, the writer believes, 

 on account of imperfect sap circulation in those parts. It is always 

 the spurs that first stop growing. Withholding water from trees 

 causes early dormancy in all the parts but the spurs are the first to 

 form terminal buds. The crude sap from the roots rises most rapidly 

 in those branches and twigs that are nearest in a straight line up- 

 wards from the ground. It would seem then, that the spurs on 

 account of their position, are deprived of water supply very early 



