142 
THE VEGETATIVE FUNCTIONS OF PLANTS 
135. Correlation within the Plant. It is of interest to 
note that the parts of a plant are not only sensitive to the 
stimulus of their surroundings, but are correlated, or ad- 
justed to each other. This correlation modifies their 
reaction to external stimulation. Thus, if the "leader," 
FIG. 101. Adjustment of leaves, by the lengthening of the petioles, to 
secure the best illumination, in maple. Top view of same branch as in 
Fig. 100. 
or main stem, of a tree is destroyed, one or more of the 
lateral branches will turn upward, in what appears to 
be an "endeavor" to perform the functions of a leader 
(Fig. 99). In other words, the destruction of the 
leader alters the mode of reaction of the lateral branches 
to the pull of gravity. 
