ae —— 
15 
The tips of the fine ultimate branches do not individually absorb with 
sufficient rapidity to give me trustworthy differences in weight, and they 
are too far apart to permit the use of several at once without a dispropor- 
tionate increase in the water to be weighed. In a single instance I was 
able to include three of them in one bottle of the usual size, and 
then the observed absorption per unit of area was about three times as 
great as I ever found it with the tips of the main roots. No far-reach- 
ing conclusions are to be based on one fortunate observation ; but it does 
show, as we must also conclude from the experiments to be described on 
transpiration, that the total absorption can be much greater than meas- 
‘urements made even on many tips of main roots would indicate. In one 
experiment, the tip of a small main root 5.5 millimeters in diameter 
showed a maximum rate for the time covered by eight weighings of 
2 centigrams per diem. 
Because of the slight difference in weight to be determined, it was 
useless, in undertaking experiments to show the relative absorption dur- 
ing different parts of the day, to work with roots which had not already 
shown themselves to be among the most active. In two sets of experi- 
ments I have used such roots for this purpose. The result has always 
been that the greatest relative absorption was observed during the after- 
noon, and, so far as any conclusion could be drawn in such detail, during 
the latter part of the afternoon. This difference, at different hours, is 
usually less marked than it appears to be from the following table, which 
shows the results for one day with the four most active roots represented 
in the preceding table. The roots bear the same numbers. This experi- 
ment began at 6.15 a. m. February 1. The figures are centigrams of 
water absorbed during the preceding interval : 
Feb. 1. | | 
| | Feb.2, | 
Root No. | , : | 6.15 
(12.15 p.m, | 6.15 p.m.) a m. 
ae eS eres eons 
eS) 5 | 5 
ny | 14 | 21 16 
Vil 10 | 19 10 
x 12 | a 17 
From the fact that decidedly the most rapid absorption is during and 
closely following the hours of most rapid transpiration, it is a reasonable 
conclusion that the tree contains practically no store of water on which 
it can easily and safely draw. However, no conclusion is justified as to 
the total water actually contained in the path of the transpiration stream, 
and therefore none as to the rapidity with which the water moves. The 
water may rise slowly but the demand still be propagated rapidly. 
My experiments on the absorption of potassium nitrate are open to 
the same criticism as pertains to all of my other absorption experiments, 
