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there are two small glass tubes bent at right angles at the extreme 

 end which are attached to a meter stick, the lower ends of which 

 are submerged in a vessel of water. One of these tubes has a 

 calibre of about three millimeters in diameter; the other of 

 about one millimeter or more. If the plant is transpiring very 



H 



L — -<! 



H 



Fig. 2. Cross-section of transpiration apparatus. T, Metal tubes holding hy- 

 grometers. H, Hygrometers. S, Springs which hold the tubes close to the leaf. 

 r. Rubber sheeting and bands. 



freely the larger tube can be used, but if transpiring only slightly 

 the smaller one will answer the purpose better, Connected 

 with the large tube containing the stem is a reservoir or supply 

 of water which is for the purpose of enabling the bubble to be 

 placed anywhere on the scale desired by letting in water or by 

 sucking it upwards. We have used this apparatus now for many 

 years with considerable success. For our purpose we attach the 

 bell-glass to a Chapman aspirator which enables one to draw air 



