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. ioi. — Adjustment of leaves, by the lengthening of the petioles, to 

 secure the best illumination, in maple. Top view of same branch as in 

 Fig. I GO. 



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. 



