i 82 
Notes . 
Ap. 19. A root 2-5 cm. diameter was cut through and mercury manometers 
attached to both ends. A rapid escape of sap took place from the end 
attached to the stem, the pressure varying from ten to fifteen feet of 
water until the fourth day when it began to fall. Practically no escape 
of sap took place from the end of the severed portion on the first day, 
but on the second, pressures equivalent to between two and three feet 
of water were shown, rising on the fourth day to nearly six feet, but 
distinctly falling on the sixth and seventh days. 
Ap. 27. The second trunk was cut across completely. No bleeding now or at 
any time. 
T wo anomalies will be noticed here. Firstly, that a higher pressure was shown 
by the attached end of the root 1 than by the severed portion, as though the ‘ root- 
pressure ' were driving the sap downwards instead of upwards; and secondly, that 
the pressure in the attached portion of the root was much higher than was re- 
quired to raise water to the cut surface of the stump, and yet no bleeding took 
place from it, although an active exudation was shown by the root. Even when 
the second trunk was cut and covered with indiarubber no actual drops of water 
exuded, although both the duramen and the remaining alburnum were quite moist. 
The explanation appears to be that, early in the year, the wood of the intact 
trunk offers a higher resistance to the passage of water than it does later on, 
although to obtain direct evidence of this is by no means easy. Furthermore, 
different portions of the root-system appear to awaken to active absorption at 
dissimilar times. Even although the pressure in the intact root-system was nearly 
uniform throughout, the maximal pressures shown by manometers attached to severed 
portions of it might vary considerably, according to the amount of absorbing surface 
and the relative activity of absorption. This is because the maximal pressure in a 
severed root always decreases sooner or later, so that the height of the pressure shown 
by an attached manometer will depend upon the rapidity with which the maximal 
pressure is attained, which again depends upon the rapidity of escape of sap, and this 
upon the activity of absorption. It would, in fact, be more accurate to test the 
pressure of absorption in a severed root by applying increasing pressures of Mercury 
until sap neither escapes nor is driven backwards. 
To perform an extended series of observations of this kind, each of which 
demands the sacrifice of a large tree, is however possible only to a privileged few. 
The above observations are therefore merely put forward as suggesting the need 
of solving the following questions : — (1) Does the total resistance to the flow of 
water in the trunk of a deciduous tree vary and show an annual rhythm or periodicity ? 
(2) Is the root-pressure comparatively constant throughout large root-systems, and 
do all regions of such systems awaken to active absorption at the same period of 
time? 
ALFRED J. EWART. 
1 The root was subsequently traced to its junction with the parent-tree. 
