52 



&OTANY. 



for turgidity is used in plant growth and in the increase of plant 

 substance. We notice when a leaf or shoot is cut away from a 

 plant, unless it is kept in quite a moist condition, or in a damp, 

 cool place, that it becomes flaccid, and droops. It wilts, as we 

 say. The leaves and shoot lose their turgidity. This fact suggests 

 that there has been a loss of water from the shoot or leaf. It can 

 be readily seen that this loss is not in the form of drops of water 

 which issue from the cut end of the shoot or petiole. What 

 then becomes of the water in the cut leaf or shoot ? 



Exercise 24. 



95. Loss of water from excised leaves. — Take a handful of fresh, green, 

 rather succulent leaves, which are free from water on the surface, and place 

 them under a 'glass bell jar, which is tightly closed below but which contains 



Fig- 43- 



Leafy shoots just covered with dry 



bell jar. 



Fig. 44. 



The same after four hours ; mist 

 shows on inside of jar. 



Figures 43, 44. — Experiment to show transpiration from leaves on cut shoots. 



no water. Place this in a brightly lighted window, or in sunlight. In the 

 course of fifteen to thirty minutes notice that a thin film of moisture is ac- 

 cumulating on the inner surface of the glass jar. After an hour or more the 

 moisture has accumulated so that it appears in the form of small drops of 

 condensed water. . Set up at the same time a bell jar in exactly the same 

 way but which contains no leaves. In this jar there will be no condensed 

 moisture on the inner surface. We thus are justified in concluding that the 

 moisture in the former jar comes from the leaves. Since there is no visible 



