Physiological Studies in Plant Anatomy 69 
Dublin, and summarised in the pages of Atkins’ monograph, has 
gone far to dispel this impression. 
When exudation pressure is being manifested the necessary 
osmotic concentration must be maintained by solutes unable to 
escape across the endodermal barrier. It is unlikely, therefore, that 
these solutes will be inorganic salts which must in the first place 
diffuse into the root through the protoplasts of the endodermis. The 
nature of the organic solutes, whose leakage into the xylem might 
be anticipated, has been discussed elsewhere (Priestley, loc. cit. 
p. 197) and the conclusion reached* that sugars and organic acids 
might be expected. The summary by Gelston Atkins already referred 
to gives an effective demonstration that sugars are usually present 
in the xylem sap, and in the course of our own experiments some 
quantitative estimations were made that support these statements. 
Experiments with the Vine (Vitis vinifera L.) 
Three large healthy vines in a temperately heated glasshouse, 
with their leaves well out, were selected. These were cut down at a 
level of about 9 inches from the ground. After chopping the stem 
through, the cut surface was levelled with a sharp knife, and any 
bits of splintered wood removed. To the stump was securely bound 
and wired a piece of an inner tube of a motor-cycle tyre and with 
this was connected a piece of glass tubing of two-inch bore. 
The vines were cut down on March 24th; one pumped up an 
average of (over) 500 c.c. sap per day for 36 days, after which the 
amount gradually decreased. The other two gave an average of 
250 c.c. per day, but had practically stopped in 28 days. 
The liquid which collected in the wide glass tubes was siphoned 
off at intervals. The first fraction collected was found to go cloudy 
on standing 24 hours, owing to the presence of bacteria, and subse¬ 
quent fractions were collected under toluol. This was effected by 
pouring a little toluol down the glass tube, the top of which was then 
plugged with cotton-wool to stop excessive evaporation. As the 
liquid accumulated in the tube it was in this way always under a 
layer of the antiseptic. When the fractions were siphoned off a little 
liquid plus the toluol was always left in the bottom of. the tube so 
that the layer of toluol never came in direct contact with the cut 
surface of the stump. The liquid was kept in Winchesters under 
a layer of toluol, and by this means was kept quite sterile. 
With this liquid quantitative investigations were carried out, to 
find the amount of organic substance present. 
