228 



PHYSIOLOGY OF NUTRITION. 



to bring deeper insight, and this is not the place to pursue the 

 subject further. We will therefore proceed to study various 

 phenomena (see 85 also as to the ease with which water moves in 

 the wood), which are at all events of great importance in helping 

 us to realise the causes of the movement of water in plants. 



We cut off two shoots of Impatiens as similar as possible, and 

 place them both with their lower ends in water. Both shoots are 

 first left for a few hours under a large bell-glass, the wall of 

 which has been moistened on the inside with water. We then put- 

 them with their cut ends in a solution of methyl green or eosin. 

 One shoot is exposed to conditions which permit vigorous tran- 

 spiration. The other we pro- 

 tect as far as possible from 

 loss of water by leaving it 

 under a bell-glass. In the 

 latter the pigment solution rises 

 only slightly, while in the 

 actively transpiring shoot it 

 rises in a short time to a con- 

 siderable height in the vascular 

 bundles. 



The effect of transpiration 

 may also be determined by 

 experiments of another kind. 

 We employ for the purpose the 

 apparatus drawn in Fig. 86. 

 By means of a piece of rubber 

 tubing a leafy shoot is con- 

 nected air-tight with a straight 

 glass tube, which is then filled 

 with water and dipped into 

 mercury. As the water is used 

 up in consequence of transpira- 

 tion, mercury enters the tube. 

 I found that during fairly 

 active transpiration it may rise 

 several centimetres in a few 

 hours (I used, e.g., shoots of 

 Lonicera tatarica). 



If in the early spring (at the 

 end of March ov the beginning of 



