Cannon : A method of measuring transpiration 



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Any bell-glass which is adapted in form and in size to the 

 plant, or branch, experimented with may be employed. Perhaps 

 the best shape for general use is that of the bell shown in figure i, 

 the enlarged upper portion of which permits the natural spreading 

 of the plant. The size of the bell is of much importance, since it 

 must correspond with the rate of transpiration. It can only be 

 told by experience. 



Figure 3. Encelia farinosa, with base constructed ol wood. The base is made 

 of two boards of which the one to the left is securely fastened to two cleats, which carry 

 buttresses on the free ends, and the one to the right is clamped into position by inter- 

 posing two w^edges between the buttresses and the loose board. By removing the wedges 

 the base is easily taken apart. 



i 



Finally, a base upon which to set the bell-glass and the poly- 

 meter must also be provided. The form may vary according to 

 the nature of the experiment. If an entire plant is under observa- 

 tion, a cement base may be used (figure 2). But this form, which 

 was originally devised to be in a measure permanent, is not alto- 



