The Water Relations of the Pine and the Silver Tree. 
17 
Water Content per cent. Fresh Weight. 
Experiment No. 3, 58-02 per cent. . Experiment No. 3, 49'66 per cent. 
„ 22, 63-93 „ . „ „ 24, 57-84 
These results are shown in graphical form in the accompanying figure : 
3 4 5 hours 
The striking difference in the behaviour of twigs of the two trees is that 
in the Silver Tree the rate of loss does not markedly fall off as the water 
content diminishes, whereas in the Pine the rate of loss falls after a few 
hours to less than one-tenth of the rate in the first hour. Tension may be 
taken to increase as the water content diminishes, unless at some point the 
resistance of the leaves begins to break down. If this happens the water 
columns in the vessels break, and the leaves lose water without being able 
to obtain fresh supplies from the stem. This may be the case with the 
Silver Tree. In the case of the Pine the bend in the curve suggests either 
stomatal or internal regulation of a far more drastic nature, and this brings 
us face to face with another difficulty — the absence of information as to the 
