CH, IV] STOMATA. 93 



decigram at a time to a scale-pan suspended to the 

 spring, 



7-5°, 7-5°, 7-3°, 7•2^ 7-0°, 7-5°, 7-2°, 7-3°, 7-5°. 

 When the whole weight was put on at once the index 

 moved through 66° of the micrometer, giving 7"3° as the 

 average value of 0"1 gram'. 



When a transpiring plant is suspended the loss of 

 weight may be read every 5 minutes with less disturbance 

 to the plant and with less labour to the observer than 

 with a balance. 



Section C. Stomata. Bloom. Lenticels. 



(117) Stomatal transpiration. 



Cut a pair of similar well-grown leaves of Ficus elastica 

 and when the bleeding of latex from the cut ends has 

 practically ceased, slip about an inch of tightly fitting 

 rubber tubing over the leaf stalk, leaving J inch of tube 

 projecting; then fold the free end down and wire it 

 tightly to the tube-covered stalk. In this way evaporation 

 from the cut end of the stalk is prevented : the wire ties 

 will also serve to hang up the leaves, and by twisting the 

 free end of the wire into a loop for one leaf and into 

 a hook for the other, obvious and permanent marks are 

 provided for the distinction of the leaves. Having weighed 

 them, hang them up close together in a dry room for 2 

 or 3 hours when they must be again weighed. These 

 weighings give the ratio between the normal transpiration 



' The springs we use are made b; Salter of Birmingham : they are 

 about 5 cm. in length, when unstretched. 



