100 TRANSLOCATION IN PLANTS 



holism hormones." For example, the accumulation of 

 food above a ring, she suggested, is due not to a check in 

 backward movement of food through the phloem but to 

 wound tissue development, callus formation, or root 

 formation which cause food to accumulate in that region. 

 The explanation is therefore the reverse of that normally 

 given. Furthermore, the low content of food below the 

 ring is suggested as due to the failure of these tissues to 

 grow, not that the failure to grow is due to lack of food. 

 The normal distribution of "cell-division hormones" and 

 the ''metabolism hormones " is upset by cutting the phloem 

 which carries them, and the abnormal distribution of foods 

 is a result of this change in hormone distribution. The 

 blocking of the xylem she also considered as partly respon- 

 sible for the failure of food to move down past a ring. 

 Experiments of her own and those of Hanstein with plants 

 having internal phloem, she considers as proof of this 

 interpretation. For example, if the outer phloem of a 

 potato stem is cut and the upper part of the shoot is 

 darkened, the shoot continues to grow above the ring, or 

 regeneration of buds occurs in this darkened part if the 

 buds are removed. Since it seemed to her that the amount 

 of internal phloem left could not carry sufficient food, this 

 must have been carried by the xylem while the necessary 

 hormones are carried in the phloem. If "cell-division 

 hormones" are produced by dividing cells and are carried 

 to new regions through the phloem, it is difficult to see 

 why, if the growing tips are not removed, growth does not 

 continue in ringed defoliated shoots where there is no 

 internal phloem. Perhaps in this case she would suggest 

 that "metabolism hormones" are necessary and that these 

 are produced only in leaves exposed to light. If this 

 latter is the case, the term "metabolism hormones" is 

 merely substituted for Hanstein's "newly assimilated sap" 

 and for which I would substitute carbohydrate. It is 

 interesting that Dixon calls upon hormones carried exclu- 

 sively in the xylem to support his hypothesis whereas 

 Kastens appeals to hormones carried exclusively in the 

 phloem to support the same hypothesis. 



