SOLUTE DISTRIBUTION AND BEHAVIOR 239 



was distinctly less marked in these defoliated regions. In 

 an experiment with Ligustrum similar to that shown in 

 Fig. 1, 20 to 21 stems were treated in each of the ways 

 indicated. Of the 20 treated as in No. 1, 4 developed 

 strong shoots just below the upper ring, with no shoots 

 elsewhere. Of the 20 treated as in No. 2 with two rings, 

 12 developed weak shoots at the node below the upper 

 ring, 5 developed weak shoots immediately above the 

 lower ring, and 4 developed strong shoots below the lower 

 ring. Of 21 treated as in No, 3, none developed w^ithin 

 the defoliated region, and 5 developed strong shoots at the 

 node below the lower ring. It seems from these and other 

 observations that a diminished absolute or relative amount 

 of carbohydrate favors shoot growth and shoot regener- 

 ation, while an increased absolute or relative amount of 

 carbohydrate favors root growth and root regeneration. 



Although regeneration of a type can be brought about 

 by changing the composition of the tissues, it can be more 

 easily brought about by cutting or otherwise inactivating 

 the solute-conducting tissue. That the interruption of 

 solute distribution alone will always account for the various 

 responses has not, however, been definitely established, and 

 one is tempted sometimes to appeal to the possible trans- 

 mission of a stimulus or hormones to account for the 

 behavior. On the other hand, I know of no undoubted 

 evidence that regeneration in plants is ever controlled by 

 hormones or by transmission effects, and since there is 

 abundant evidence that cutting, or otherwise inactivating 

 the phloem, does interfere with the transport of nutritive 

 materials, I rather hesitate at accepting the hypothesis, 

 more easily formulated than proved, that regeneration 

 phenomena are controlled by hormones, by specific growth 

 substances or by transmission of influences of one sort or 

 another. 



42. Relation between Solute Distribution and Domi- 

 nance. — Almost inseparable from problems of regeneration 

 are problems of dominance. No simple explanation has 

 been offered to solve the problem of competition between 



