98 NEW ZEALAND NATURE-STUDY BOOK 
a 
and, moreover, should be removed from that portion of the 
stem above the level of the water. In spite of the removal 
of the bark, the water will continue to 
travel up the stem and into the leaves, 
as is apparent from the fact that the 
leaves do not wither, but continue green 
and fresh. The base of the stem, in fact, 
continues to absorb water, which grad- 
ually passes up through the woody 
portion of the stem and finally into the 
leaves through the mid-rib and smaller 
nerves. 
In the case of a soft stem, ¢9., that 
of a Sun-flower, which has no general 
woody body, but possesses bundles of woody tissue, the 
liquid passes up through these, which form the food 
channels. 
The same results would be obtained by using a plant 
with roots instead of a branch as shown. 
Transpiration. The passing away of water in the 
form of vapour from those parts of the plants which are 
exposed to the air is known as transpiration. 
That water does pass away from the plant can be 
demonstrated by the following experiments :— 
(a) Take a potted plant and carefully cover with a 
piece of tinfoil the earth in the pot, in such a way as to 
prevent, or at least minimise, the evaporation of water 
from the soil. Carefully weigh the pot and its contents, 
and after the lapse of an hour or two weigh again. It 
will be found that the weight has decreased ; for the soil 
has lost water by transpiration through the leaves of the 
plant. The decrease in weight does not represent the 
whole amount of water transpired, for the plant has gained 
shghtly in weight owing to the carbon obtained from the 
