CHAPTER IV. 



TRANSPIRATION, OR THE LOSS OF WATER BY 

 PLANTS. 



68. We should now inquire if all the water which is taken up 

 in excess of that which actually suffices for turgidity is used in the 

 elaboration of new materials of construction. 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 flac- 

 cid, 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 ? 



Pig. 46. 

 To show loss of water from leaves, the leaves just covered. 



69. Loss of water from excised leaves. Let us take a handful 

 of fresh, green, rather succulent leaves, which are free from 



35 



