28 TRANSLOCATION IN PLANTS 



After many of these ringing experiments had been com- 

 pleted it was found that Hanstein (1860) had carried out 

 similar experiments and had obtained similar results. He 

 concluded, however, that lack of water cannot be the 

 cause of the withering, for when leaves remain above 

 the ring, certainly more water is necessary than when the 

 leaves are absent but growth continues, while the shorter 

 the part above the ring the less water it will need but the 

 quicker is its death even in a moist chamber. 



Hanstein explained this lack of growth or death above a 

 ring when the leaves are removed as due to a lack of 

 "freshly assimilated sap." He seems to have accepted 

 Hartig's idea (1858) that carbohydrates and other products 

 stored in the xylem are carried through the xylem but 

 thought that materials stored in the phloem and ''freshly 

 assimilated sap" move in the phloem only. When leaves 

 remain above a ring, they were supposed to supply this 

 special material. Hanstein also observed that ringed wil- 

 low cuttings placed in dry air showed a withering of the 

 phloem above the ring, while the presence of leaves in this 

 region prevented withering. He concluded that water 

 cannot move readily from xylem to phloem and that leaves 

 aid in this transfer. According to his ideas, therefore, 

 the leaves supply ''freshly assimilated sap" which is 

 necessary for growth and can be carried through the 

 phloem only, and they aid also in transmitting the water 

 to the phloem when the latter is separated from the roots 

 by a ring. Hartig (1862) disagreed with Hanstein's inter- 

 pretation and suggested that the failure of defoliated shoots 

 to grow in a dry atmosphere was due to drying out of the 

 wood at the point of injury, and their failure to grow in a 

 saturated atmosphere was due to failure of the water stream 

 to move. 



If, on the other hand, all solutes including sugars are 

 carried through the phloem chiefly and not through the 

 xylem, ringing would check continued growth by with- 

 holding the necessary solutes, while the withering might 

 be due not to the lack of any particular solute, but to a 



