424 BOTANICAL GAZETTE [JUNE 
through which air left the jar, extended only about 1 cm. inside 
of the stopper. Tube 2 was connected with rubber tubing to a 
glass-stoppered calcium chloride tube (B). The calcium chloride 
tubes were accurately weighed at the laboratory before and after 
each experiment. The ground stoppers (3, 3), when turned, 
effectually closed the tubes. 
The aspirator for drawing air through the apparatus was a bottle 
of 19 liters capacity fitted with a siphon through which the flow 
\ = 
C CHCrobill 
Fic. 1.—Apparatus for measuring transpiration: explained in text 
could be regulated by means of a screw clamp (4). Three sets of 
apparatus were constructed and carried in a spring wagon which 
could be moved from tree to tree as occasion required. 
The manner of conducting an experiment was as follows. The 
apparatus was placed at a tree where direct rays of sunlight would 
not strike it. A twig bearing leaves suitable for experiment was 
selected and inserted in the cleft rubber stopper, precautions 
against bruising or injuring the bark being used. In some cases 
one or two leaves had to be removed from the twig in order to make 
a good adjustment. After a few trials it was found that not more 
