UPWARD TRANSLOCATION OF FOODS IN WOODY PLANTS 1 23 
the vessels. If this were true, one would expect a depletion of carbohydrates 
below a ring in the maple, especially when it is ringed during the season of 
sap flow and when the ring is only one to two centimeters broad. 
A possible frequent interposition of living cells across conducting tubes 
may readily prevent a flow of solution, and the water may normally move 
largely by diffusion. When a tissue is cut, however, as in pruning or in 
tapping, there is probably an actual flow of solution through the opened 
vessels which might also result in a depletion of storage materials from adja- 
cent tissues. The movement of water through uninjured xylem may 
occur chiefly by diffusion as in the case of the entrance of water from the 
soil into a root. In the latter case there is certainly no flow of solution, as 
the amount of water taken up has no relation to the amount of solutes 
absorbed. Data reported by Kiesselbach (191 6), who grew plants in soil, 
indicate that increased transpiration does not increase ash absorption. 
Experiments by the writer in collaboration with Dr. E. Artschwager and 
Dr. N. B. Mendiola, that are nearly ready for publication, show that 
doubling the transpiration from plants growing with their roots in nutrient 
solutions has no tendency to increase salt absorption. 
It may even be that at least some of the mineral nutrients move pri- 
marily through the phloem. It is true that, if a stem is placed in a solution 
of dye, the dye will rise rapidly through the xylem, but whether it will do so 
in a normally rooted plant has not been conclusively proven. The writer 
has found, however, that lithium chloride applied to a rooted plant will 
move through the xylem past a ring. It is possible, however, that it was 
not carried in the "transpiration stream" but rather that it moved past 
the ring by diffusion. Lithium salts will diffuse much more rapidly than 
sugars, and cell membranes seem to be very permeable to them. iT*he 
lithium was found in the phloem and cortex above the ring as well as in the 
xylem. 
A number of papers have been published in which it has been shown that 
certain dyes or salts appear to travel in the "transpiration stream" through 
the xylem when the roots of the plant are placed in the solutions. But in 
many cases the dyes or salts used may have had toxic effects as a result of 
which the cells that might normally retard their movement may have been 
killed or their permeability may have been increased. Furthermore, it 
has been found in a number of instances that the solutes appeared to travel 
at about the same rate in the phloem region as in the xylem. Bokorny 
(1890) found that, when roots were placed in solutions of iron sulphate or 
of various dyes and the leaves were exposed to very drying conditions, the 
solutes were found in the phloem region at about the same height as in 
the xylem region. When on the other hand a cut stem was placed in the 
solution, the movement through the xylem was distinctly the more rapid. 
Because he always found the solutes not in the lumina but in the walls of the 
thicker-walled elements, such as the vessels, sclerenchyma, and collenchyma 
cells, Bokorny came to the conclusion, which has since been clearly dis- 
