MacDougal : Some Correlations of Leaves 509 



the newly formed branches were enclosed and in the winter con- 

 dition. My absence from the Garden during July prevented obser- 

 vations being taken during a period of four weeks, but an exami- 

 nation of the plants on July 30 showed that all of the newly formed 

 delaminated branches of this season had perished and that buds on 

 the older branches had awakened and extended to a length some- 

 thing less than the normal growth of the earlier part of the season. 



The increase in the amount of chlorophyl in the cortex may be 

 considered as a further effort to meet the losses ensuing from the 

 lack of the laminar portions of leaves. The non-development of 

 the phellogen and the imperfect construction of the bast fibers and 

 fibrovascular bundles may be ascribed in part to a lack of formative 

 material and in part to the absence of the stimulation ensuing from 

 the decreased transpiration stream and the material usually formed 

 in the laminae. In addition, the mechanical strains and stresses 

 e.xerted by the foliar organs undoubtedly exert some stimulative 

 effect on the rigidity and pliability of the stems by the induction of 

 the development of various mechanical elements. The absence of 

 stimuli of this character would account in part for the imperfect 

 development of the stems. 



The tests with Ac\r were much more restricted. The petioles 

 were excised near the base and the effect upon the activity of the 

 vegetative points noted. Only a single basal branch of a small 

 tree was treated in this manner, and comparisons were made with 

 corresponding portions of similar branches arising from the same 

 part of the central stem. 



The single normal branch taken for comparison developed 

 four internodes which had a diameter about thirty per cent, greater 

 than the internodes of the defoliated branch. The total length of 

 the four newly formed internodes amounted to 78 mm., the longest 

 being the third from the base of the yearly growth, measuring 25 

 mm. Eight active functional leaves were developed. (One has 

 been cutaway in the illustration,/. 2, A.) The newly-grown part 

 of the defoliated branch measured 48 mm. and comprised seven 

 internodes, the longest of which was the sixth from the base, 

 measuring 8 mm. The excision of the leaves had induced the de- 

 velopment of one bud in the axil of the last internode of the 

 previous season. The branchlet thus formed showed two long 



