36 TRANSLOCATION IN PLANTS 



burger (1891, p. 900) claimed that food moved to these 

 fruits through the xylem. Miinch found, however, that 

 if precautions were taken to cut all the phloem leading to 

 the fruits, they were unable to receive food from the leaves 

 below. Since the young fruits are green, he also tested the 

 influence of light and darkness on the development of such 

 fruits on ringed stems. The results indicated clearly that 

 most of the food comes to the fruits from other parts of the 

 plant and that this is transported through the phloem. 



9. The Effect of Cutting the Xylem on the Transport of 

 Solutes. — Dixon (1922) and others have claimed that the 

 reason why ringing interferes with solute movement is 

 that the ringing results in a plugging of the xylem by 

 tyloses or gums or otherwise interferes with its activity. 

 Though positive evidence has been obtained that such 

 plugging does not always occur, and in fact rarely occurs 

 if the ring is made carefully and the ring wound well 

 protected, yet to settle the question finally it would be 

 desirable to carry out experiments in which not merely the 

 phloem is cut and the xylem left intact, but in which 

 the treatment is reversed and the phloem is left intact and 

 the xylem cut. It is more difficult to carry out the latter 

 type of experiment for obvious reasons. The xylem being on 

 the inside of a hollow cylinder cannot be cut out without 

 some injury to the phloem outside. Its removal also 

 involves the removal of a tissue conducting water to the 

 parts above, which is perhaps the greatest difficulty, and 

 it also removes the support for the parts above. 



As previously reported in some detail (Curtis, 1925), 

 various methods were used for supplying the upper part 

 of the shoot with water when the xylem was cut and the 

 phloem was left to bridge the gap. The only uniformly 

 successful method was that in which the operated part of 

 the stem was encased in a tube open at both ends. A 

 water-tight joint was made with the stem at the lower end 

 of the tube by means of a split cork sealed to the stem and 

 to the tube with melted paraffin. This tube, when filled 

 with water, served to supply the shoot above with water 



