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. 



