278 TRANSFER OF WATER THROUGH THE PLANT. 



is replaced by direct sunlight, the increase in transpiration is 

 striking. 1 



744. Effects of different rays upon transpiration. Wiesner's 

 conclusions, 2 based on a study of transpiration in different rays 

 of the spectrum, are as follows : (1) the presence of chlorophyll 

 appreciably increases the action of light upon transpiration ; 

 (2) it is the rays corresponding to the absorption-bands of 

 chlorophyll, and not the most luminous rays, which cause trans- 

 piration ; (3) rays which have passed through a solution of 

 chlorophyll have only a feeble effect upon the process ; (4) the 

 non-luminous heat-rays act as do the luminous rays, but in a 

 less marked manner, the ultra-violet chemical ra}'s have sub- 

 stantially no effect ; (5) whatever the rays are, they always act 

 by elevating the temperature of the tissues. 



745. Effect of shock upon transpiration. 8 According to Bara- 

 netzky, 4 shaking a plant for a short time increases transpiration 



1 As shown by the following experiments by Wiesner : 



The amounts of water are calculated for a surface of 100 square centimeters, 

 and for one hour. But it is not perfectly clear to what the special action of 

 light can be due. The increased size of the cleft of stomata under light cannot 

 account for all cases ; for according to Wiesner young maize plants, in which 

 the transpiration is large, have their stomata closed. 



2 Annales des Sc. nat., ser 6, tome iv., 1877, in which may be found also a 

 note upon the same subject by Deherain. 



8 See also Herbert Spencer's Experiments, on page 263. 



4 Botanische Zeitung, 1872, p. 89. 



The following example will show the results of Baranetzky's experiment 

 upon a leafy stem of Inula Helenium. 



