m 



IRANSPIRAXIOX OF PLANTS. 



93 



red glass rauged from 59^ to 64° ; wliile that for the same plant 

 under yellow glass was from 59*^ to 62° ; and yet in this instance 

 the yellow glass gave a rather higlier loss than the red. Again, 

 for No. II., the temperature for red glass varies from 59° to 60°, 

 that for yellow from 59° to 61°, showing that in both cases the 

 temperature was loicer, when the loss was comparatively greater, 

 contrary to what would be expected, since it is known that an 

 elevation of temperature is one of the causes of increasing the 

 loss of moisture. The differences, therefore, must be put down 

 to the unascertainable variations in the amount of sunlight. 

 Hence will be seen the importance of a protracted series of 



experiments; and the results given under the line of ** Totals" 

 will undoubtedly be a much nearer approximation to the truth. 



These give one maximum for the red, and another for blue and 

 violet, together ; while yellow and green together furnish a 

 decided maximum. 



An independent maximum is also supplied by clear glass. 

 Comparing this with the effects of the yellow glass, which also 

 transmits red light, it seems that so far from the optically 

 brightest rays being a chief cause of transpiration, the yellow, and 

 those ravs on the more-refrangible side of it, where the chloro- 

 phyll absorption-bands, viz. Nos. II., ]II., and IV., are feeblest, 

 'tnust have actually a retarding influence upon the effect of red 

 and violet lights^ which ^i?r se are most powerful. 



Lettuces (second series). 



No. 



E. 



1 



Y. 



r 



G. 



B. 



V. 



CI. 



I 



II 

 III 



IV 



V 



VI 



Totals... 



1-13 



•81 

 1-22 

 1-89 



•92 

 1-93 



7-90 



1-05 

 •54 

 120 

 110 

 1-35 

 r40 



104 ; 



102 



112 



1-87 



■97 



129 



llo 

 •33 



1 •fjO 



1-54 

 •73 



1-50 



675 



1^42 

 1-08 

 1-55 

 1-59 

 1-20 

 241 



154 



•68 

 1-35 



139 



1-33 



1-58 



6-64 



7-31 



9-25 



7*87 



The temperature for the six days ranged from 57° to 60°. 



As in the preceding series, one maximum occurs under the red, 

 another under the violet or most-refrangible end, while yellow is 



a minimum. Green gives a rather higher result than 

 before. Combining the two series, the mean of the two totals 

 is as follows : 



a gam 



R. 



7-21» 



Y. 



6-39 



G. 



6*98 



B. 

 6-70 



V. 



9-49 



CI. 

 7-37 



