278 TRANSFER OF "WATER THROUGH THE PLANT. 



is replaced by direct sunlight, the increase in transpiration is 

 striking.^ 



744. Effects of different rays upon ti'anspiration. Wiesner's 

 conclusions,^ based on a study of transpiration in different raj-s 

 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 

 chlorophj-11, 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 rays have sub- 

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

 b}' elevating the tempei-ature of the tissues. 



745. Effect of sliock upon transpiration." According to Bara- 

 netzk}-,* shaking a plant for a short time increases transpiration 



1 As shown b}' the following experiments hy Wiesner : — 



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

 and for one hour. But it is not Yierfeotly clear to what the special aetionof 

 light ca7i be due. Theinp»»Se3 size of the cleft of stomata under liglit cannot 

 account for all oases^^or according to Wiesner young maize plants, in which 

 the transpiratii^rts large, have their stomata closed. 



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

 note ui^5h the same subject by Deherain. 



5 See also Herbei-t Spencer's Experiments, on page 263. 



* Botanische Zeitung, 1872, p. 89. 



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

 upon a leafy stem of Inula Helenium. 



