508 MacDougal : Some Correlations of Leaves 



The enlarged stipules exhibited a thickness four or five times 

 as great as the normal, chiefly due to increase in tissues and dif- 

 ferentiations toward the structure of a typical lamina. A median 

 layer of loosely arranged parenchymatous tissue contained much 

 chlorophyl which was almost wholly lacking from the normal 

 organ. This mesophyllary tissue also exhibited numerous inter- 

 cellular spaces, and was altogether well adapted to carrying on 

 photosynthetic and transpiratory functions. 



The entire stipule, which is usually closely appressed to the 

 petiole, was held at a more widely divergent angle than the normal. 

 These adaptations have greater significance when it is understood 

 that the total amount of stipular surface presented by a delami- 

 nated branch would amount to about fifteen or sixteen times as 

 much as the normal. This comparatively normal increase, how- 

 ever, does not result in developing a foliar surface of more than 

 one or two per cent, of that of the normal leafy branch. 



Sections of the sixth internode from the base of the twigs 

 formed in 1903 were examined in order to ascertain the effect of 

 deprivation of the laminar structures and their partial replacement 

 by the stipules. It has already been pointed out that the branches 

 which had been delaminated had developed more internodes, the 

 total lengths of which were less than of twigs normally grown, and 

 had the appearance of being slightly thicker, but no measurements 

 were made which might form the basis of an exact comparison. 

 The epidermal tissues of the treated branch had greater radial 

 and tangential diameters, and the underlying collenchymatous 

 layers were but slightly thickened. The medio-cortex contained 

 much more chlorophyl than the normal. The bast fibers were 

 not so heavily thickened as in the normal, and the walls of all the 

 internal tissues exhibited a slight yellowish tinge. The cambium 

 showed a greater number of layers than the normal. The xylem 

 was irregularly developed and seemed to have attained a less 

 •advanced stage of differentiation in its various elements than in 

 the normal. The tangential development was notably deficient 

 and the separate bundles were separated by wide rays of pith. 



On June 1 5 the delaminated branches had assumed the appear- 

 ance of a resting stage. The formation of leaves had ceased, and 

 nearly all of the stipules had fallen off The buds in the axils of 



