130 TRANSLOCATION IN PLANTS 



more reasonable to interpret the experiment as proving 

 that the narrow bridge of phloem is carrying the sugar, 

 nitrogen, or ash, rather than that it is preventing a stoppage 

 in the xylem and thus allowing it to be carried in the narrow 

 bridge of xylem. 



It is interesting that a large number of writers unhesi- 

 tatingly accept the evidence from ringing experiments to 

 the effect that organic matter is carried in the phloem but 

 balk at the same type of evidence when it is interpreted 

 as demonstrating transport of salts through the phloem. 



Although I am convinced that the hindrance to trans- 

 port past a ring is not due to increased resistance to flow, 

 the criticism still remains that, possibly through an indirect 

 effect of accumulated carbohydrates on transpiration, the 

 actual rate of flow through ringed stems may be lessened. 

 This point is discussed in Sec. 13. 



Some have hesitated to accept the evidence obtained 

 from ringing experiments because they felt that ringing 

 has altered growth, and the altered growth has been the 

 cause of the changed solute distribution, not the result. 

 Such is evidently the contention of Kastens (1924), Hooker 

 (1924), and Swarbrick (1927), while others in conversation 

 have expressed similar doubts. It seems that these doubts 

 are really due to the fact that their previous assumptions 

 were wrong. For example, Kastens, assuming that solutes 

 must move through the xylem, because the phloem seems 

 inadequate, explained behavior as due to lack of specific 

 hormones. Hooker (1924) and others, assuming that salts 

 and nitrogen must be carried through the xylem, explain 

 the deficiency of nutrients above the ring as a result of the 

 poor growth, not the cause. Hooker evidently overlooked 

 the fact that ringing interferes with salt and nitrogen move- 

 ment not only in the cases where the ringing was done 

 before shoot growth was completed, but in a large number 

 of cases when the ringing was done after terminal growth 

 and enlargement of leaves had ceased. Some seem to have 

 in mind that this altered growth is due to an interference 

 in the movement of ''hormones," or "inhibitors" or 



