THE RANGE OF DOMINANCE . i6i 



cerned. If this dominance and the dominance of the 

 stem-tip both result from metabolic gradients, then 

 there must be in plants possessing roots two metabolic 

 gradients in opposite directions, the apical region of one 

 being in the stem-tip or tips, that of the other in the 

 root-tip or tips. 



Two gradients in opposite directions along the same 

 axis cannot exist at the same time without interfering 

 with and partially obliterating each other unless they 

 have different paths of transmission or are of different 

 metabolic character. Concerning the possibility of the 

 simultaneous transmission of different metabolic changes 

 in different directions in the same protoplasm we know 

 nothing, and our knowledge of conducting paths in the 

 plant does not go far beyond the fact that some part of 

 the vascular bundles seems to transmit some kind of 

 change better than other tissues. 



It is possible, however, that the influence of the root 

 system on the stem as a whole may be different in 

 character from the dominance of the main root-tip on 

 lateral roots. This possibility is suggested by the fact 

 that the range of dominance within the root system is 

 rather short, even where the tissues are differentiated, 

 while the apparent dominance of the root system as a 

 whole over the stem and other parts of the plant is 

 apparently unHmited in range or without relation to 

 distance. The root system takes up water and nutri- 

 tive salts and these are transported to other parts of 

 the plant. It is conceivable that the inhibiting influ- 

 ence of the root system on the formation of roots in other 

 parts of the plant may be rather a transportative than a 

 transmissive correlation, and that the other parts give 



