FRANK E. GARDNER 221 



controls. No mention was made of injury from the sprays. Mitchell 

 and Cullinan (31) failed to confirm these promising results with peaches 

 by using sprays applied in the spring. While the leaf buds were retarded 

 the flower buds were either injured by the high concentrations of 

 the growth substances or were not delayed in opening. Hitchcock and 

 Zimmerman, working with peaches and several other fruits, reported 

 (22) that a more effective time to apply the growth substances is during 

 the preceding summer when differentiation of the flower buds takes 

 place. Their report was most encouraging and did not emphasize any 

 injurious effects from the high concentrations of the potassium salt 

 of NAA used at this time of year. From subsequent work on peaches 

 Marth, Ha vis, and Batjer (29), using the same compound at the same 

 concentration range and same time of year, concluded that injury to 

 buds and even to branches is so severe as to preclude use of this compound 

 as a possible orchard treatment. Moreover, the delay in flowering was, 

 at the best, only two days; and according to these workers, it was 

 probably associated with injury rather than an inhibiting effect of the 

 sprays. Usually the critical test of the feasibility of any suggested orchard 

 practice is whether or not fruitgrowers adopt it. Growth substance 

 applications for delay of flowering in fruit trees have not reached that 

 stage, but certainly the importance of the problem warrants more 

 investigation. 



Breaking of dormancy. — In determining the southern limits of decidu- 

 ous fruit culture probably no factor is more important than the chilling 

 requirements necessary to terminate the rest period of the trees. During 

 mild winters at the present southern limits of these fruits the chilling 

 requirements may not be satisfied, with the result that the trees and their 

 potential crops suffer from delayed foliation. It is not unlikely that 

 dormancy involves a hormone relationship. The work of Bennett (8) 

 points to a high auxin content in buds and shoots of pear trees as the 

 dormant condition is entered, and a progressive disappearance of the 

 auxin as the rest period is gradually broken. The growth-inhibiting 

 effect of applied synthetic hormones on vegetative buds, particularly 

 the effect of these compounds in maintaining dormancy of tubers, 

 further supports a relationship between hormones and rest period. 

 Obviously here is a problem in which it would be desirable to accomplish 

 the opposite of prolonging dormancy. It is possible that to accomplish 

 this end compounds may be necessary that have quite a different physio- 



