SOLUTE DISTRIBUTION AND BEHAVIOR 237 



titious. Exceptions will, of course, be found in some plants 

 which seem incapable of regenerating shoots or roots. 

 Although many of the responses to ringing, especially 

 changes in food content, diameter growth above and below 

 rings, growth of fruits, storage organs, and roots, obviously 

 result from an interruption of food transport and have 

 been usually so explained; other explanations have fre- 

 quently been offered to account for regeneration phe- 

 nomena. Some have proposed that regeneration or its 

 lack is controlled by inhibitors (Loeb, 1919; Reed and 

 Halma, 1919a, 19196) or hormones (Kastens, 1924) which 

 are supposed to be carried in the phloem. Others have 

 attempted to explain the phenomena on the basis of the 

 transmission of a stimulus or influence through the phloem 

 (McCallum, 1905; Child, 1921). Still others have con- 

 sidered that movement of nutrient materials (Loeb, 1924) 

 may largely control the regeneration phenomena. I shall 

 not attempt to discuss these interpretations at length or 

 to weigh the evidence for and against them, but whatever 

 interpretation is considered, it should be clearly recognized 

 that cutting the phloem, though it may cut the channel 

 through which specific hormones or inhibitors may be 

 transported or through which a stimulus may be trans- 

 mitted, it at the same time severs the tissues through 

 which normal solutes, sugars, proteins, and salts are being 

 or can be carried. Furthermore, it not only prevents 

 backward movement of solutes from the leaves but move- 

 ment toward the apex also. Reed and Halma (1919a) 

 and Child (1921) failed to realize this possible upward 

 transport through the phloem. 



Loeb (1924, pp. 137-139) claimed that the materials that 

 influence the mass of regenerated tissue move in both 

 directions past a region that has been ringed. In experi- 

 ments to test this point, with Bryophyllum, the plant 

 Loeb used, I have been unable to duplicate his results 

 when the phloem was entirely cut. In ringing Bryophyllum 

 I have found that it is easy to remove an outer layer con- 

 sisting largely of cortex, which treatment gave the stem 



