June, 1921] 
CHILD — PHYSIOLOGICAL CORRELATION 
Finally it may be noted that in the bean seedling the rate of reaction 
of the buds of the different axils to physiological isolation by a cooled zone 
differs according to the level of the plant. With a cooled zone of given 
length and given temperature at a given distance above the node concerned, 
the buds of a more apical node begin to grow earlier and grow more rapidly 
than those of a more basal node. This fact also seems to me to offer diffi- 
culties to the hypotheses of dominance by means of inhibiting or by means 
of nutritive substances. On the other hand, it is apparently an expression 
of the physiological gradient, the primarily quantitative gradation in phy- 
siological condition along the plant axis, which, as I believe, is the basis of 
physiological correlation in the plant. In other words, the relation of 
dominance and subordination is also an expression of the physiological 
gradient, and the movements of substances in the plant are not the primary 
factors in physiological correlation, but rather the consequences of the 
differences which constitute the physiological axial gradient. 
