LIVING PARTS OF THE STEM LEP 
Plant-food is made out of the raw materials by the leaves, 
and so the more leafy side of a tree forms thicker rings 
than the less leafy side, as shown in Fig. 79. 
119. Rate of Movement of Water in the Stem. — There 
are many practical difficulties in the way of ascertaining 
exactly how fast the watery sap travels from the root to 
the leaves. It is, however, easy to illustrate experimen- 
tally the fact that it does rise, and to give an approximate 
idea of the time required for its ascent. The best experi- 
ment for beginners is one which deals with an entire 
plant under natural conditions. 
EXPERIMENT XXII 
Wilting and Recovery. — Allow a fuchsia or a hydrangea! which 
is growing in a flower-pot to wilt considerably for lack of watering. 
Then water it freely and record the time required for the leaves to 
begin to recover their natural appearance and position, and the 
time fully to recover. 
The former interval of time will give a very rough idea 
of the time of transfer of water through the roots and the 
stem of the plant. From this, by measuring the approxi- 
mate distance traveled, a calculation could be made of the 
number of inches per minute that water travels in this 
particular kind of plant, through a route which is partly 
roots, partly stem, and partly petiole. Still another 
method is to treat leafy stems as the student in Exp. XXI 
treated the twigs which he was examining, and note care- 
fully the rate of ascent of the coloring liquid. This plan 
is likely to give results that are too low, still it is of some 
use. It has given results varying from 34 inches per 
1 Hydrangea hortensia. 
