Notes. 
559 
the gauge, as by forcing the rod into the bottle the water is driven 
out along the capillary tube. 
As a preliminary, two marks are made on the gauge tube at a 
known distance apart ; the capillary tube is also calibrated by filling 
with mercury and weighing; in the example figured the distance 
between the marks is 50 cm,, and r cm. of the capillary tube contains 
Fig. 9. 
The stem of the shoot selected for experiment is pushed through 
the hole in the stopper, the bottle filled with distilled water and the 
stopper inserted, excluding any air-bubbles ; after a few minutes 
the rod is gently screwed into the bottle till the water in the capillary 
tube is forced past the mark. The water begins to recede in the 
tube as it is absorbed by the shoot; the time is noted that elapses 
as the water recedes from the first to the second mark. The water 
can then be forced back to the zero and a new determination made 
under varying conditions of temperature, illumination, &c. Finally, 
the area of the leaves can be ascertained by tracing them on to 
squared paper. 
