USE OF THE SPECTROSCOPE IN STUDY OF PLANT LIFE. 93 



agTeement of their results with those of other plants treated in the 

 same way. 



Cactus. 



A small specimen of a cylindrical cactus, growing in a pot and 

 protected as described, gave the following results: — 



No. 



R. 



T. 



a. 



B. 



Y. 





Range of temp. 



I. . 



•12 



•11 



•07 



•08 



•05 



•12 



44°- 52° 



XL . 



•01 



•15 



•04 



•16 



•05 



•10 



40°— 53° 



III. . 



•18 



•27 



•10 



•17 



•12 



•14 



54°— 63° 



IV. . 



•13 



•25 



(?) 



•07 



•23 



•03 



54°— 61° 



V. . 



•22 



•14 



•21 



•03 



•26 



•15 



55°- 64° 



VI. . 



•18 



•17 



•15 



•21 



•12 



•07 



54°— 60° 



Total . 



•84 



•99 



•57 



•72 



•83 



•61 



44°— 64° 



Mean . 



•18 



•16 



•11 



•12 



•14 



•10 



54" 



In this case yellow glass gives a higher loss than red ; and as 

 this also occurred with box, and with one of the palm series, but 

 with neither of the lettuce series, one is led to imagine that the 

 character of the epideraiis may be an important factor, and alter the 

 effect of the light. 



Fern. 



A small fern, apparently a species of Asplenium , was experimented 

 with, simultaneously wuth others. It gave the following results: — 



No. 







Y. 



G. 



B. 



■ Y. 



CI. 



I. . 



•78 



•77 



•86 



•72 



•77 



•83 



II. . 



•87 



•66 



•83 



•60 



•79 



•50 



III. . 



•76 



•86 



•62 



•65 



•67 



•75 



IV. . 



1-54 





•84 1 



M5 



1-03 



1-33 



Total 



8-95 



2-96 



315 ' 



8^12 



8-26 



3^41 



Mean 



•99 



•74 . 



•79 



•78 



•81 



•85 



This result obviously agrees with the preceding. 



The above experiments, selected from a large series, seem to me 

 to abundantly prove that Wiesner's results are correct; and, while 

 recognizing the fact that obscure heat-rays cause a certain amount of 

 the loss of water by evaporation, that transpiration per se (theoretically 

 distinct from the purely physical process of evaporation, which takes 

 place from all moist surfaces and bodies, dead or alive) is especially, 

 if not solely, referable to those particular bands of light which are 

 absorbed by chlorophyll, and that such light, being arrested, is con- 

 verted into heat, which then raises the temperature within the tissues 

 and causes the loss of water. 



I am not aware of any attempts to ascertain the exact amount of 

 difference between evaporation, due to heat alone, and to transpira- 



