Lecture 4 — 73 — Movement and Distribution 



Then a later development represented a swing of 

 the pendulum in the opposite direction. The idea was 

 sometimes advanced that movement of salt and of 

 water had no definite relationship. In general the 

 earlier teaching and the one that still prevails, was 

 that the salts move upward in the dead conducting 

 elements of the plant in the xylem tissues, along with 

 water, but several investigators have not accepted 

 this as the chief path of movement of salt and pro- 

 posed instead that the main path of upward trans- 

 location may be in the living cells of the phloem. 

 There also has long been discussion of the problems 

 of secondary movements of solutes in living cells of 

 the phloem and of the distribution of nutrient salts 

 in various parts of the plant. This phase of the subject 

 would require special treatment. 



Metabolism and Salt Absorption and Movement — 

 relations of water absorption to salt absorption : — I 



wish now to leave these broad questions in temporary 

 suspense while I cite a number of simple experiments 

 which may perhaps bring into sharper focus several 

 aspects of the absorption and translocation of inor- 

 ganic solutes. Concerning the general relations of 

 water and solute absorption certain facts presented 

 in the previous lecture should be recalled. They made 

 clear that excised barley roots may have a high ca- 

 pacity for salt absorption and accumulation over lim- 

 ited intervals of time, during which the roots maintain 

 a suitable metabolic activity by the utilization of or- 

 ganic substances previously stored. There are even 

 instances of the absorption during a short time of 

 nearly the same amount of salt by excised roots as 

 by corresponding intact, transpiring plants. It is 

 apparent, therefore, that the absorption of salt and 

 the absorption and transpiration of water are in this 

 respect independent processes. The continued absorp- 

 tion of salt is nevertheless dependent on the functions 



