266 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I4O 



known evidence of diameter flushes being predetermined as is possibly 

 the case with tip flushes. Then, too, there are cases of two diameter 

 flushes to one tip flush, and one diameter flush to two tip flushes. 



The problem of growth-hormone effects resembles that of genetic 

 effects in that the hormones shift emphasis away from the more ob- 

 vious and immediate physiologic factors, as controlled by environment, 

 to those factors less obvious and more remote. If hormones alter- 

 nately promote and inhibit growth, we must search out factors con- 

 trolling hormone growth rather than factors directly controlling cam- 

 bial activity, differentiation, and maturation. Those ecologic factors 

 which students have been investigating may apply to either case. 



Multiplicity, or the tendency toward, can be induced apparently by 

 factors local to a single tree ; for instance, excessive drainage toward 

 or away from the tree, competition, temperature pocket, or soil condi- 

 tions. In the case of the trees TTAp i and TTAp 2, the second was 

 irrigated July 25, 1939, and added a second growth layer as well as a 

 second tip flush, whereas TTAp i, not irrigated, did not add extra 

 flushes. MacDougal (1936) had performed the same type of experi- 

 ment at Carmel, Calif., with like results. 



Trees from the Texas Agricultural Experiment Substation yielded 

 extreme multiplicity because of periodic irrigation. For instance, XSC 

 1-3-a, 70 cm. from tip of branch, contained 15 sharply bordered 

 growth layers for four years. Although the multiplicity may be an 

 exaggeration, it is just this exaggeration which teaches what a tree can 

 and will do under certain habitat conditions. Branches, of course, 

 could have effects exaggerated in contrast with the trunk, but available 

 evidence does not support such a view. 



A more simple nonclimatic cause of growth variation is suggested 

 by a pear tree, 4 feet high, which grew within a few feet of the Wash- 

 ington series of trees. It had grown a second set of blossoms by May 

 13, 1945, the first set having been frozen subsequent to April 25. A 

 year prior to this. May 13, 1944, the pear tree was carrying six pears 

 and had tip growth of i cm. On the same date in 1945, it had no pears 

 but had tip growth of 45 cm. The production of fruit, identical with 

 a heavy seed year in other trees, may well retard growth. 



MULTIPLICITY AND CHRONOLOGY 



The effect of multiplicity upon all problems having to do with chro- 

 nology is a serious matter indeed. It seems clear from the evidence 

 available that multiplicity exists in the lower forest-border region and 

 also that the "factor of multiplicity" varies with the habitat. 



