94 



REV. G. HENSLOW OX THE 



This result clearly shows the preponderating effects of the red 

 and violet ends of the spectrum ; and tliey are of course just 

 where the strongest chlorophyllian absorption-bands occur. 



Clear glass gives a decided maximum, though in mauy cases 

 the loss is less than under violet aloue ; hcuce I would repeat, 

 and I believe the observation has not been made before, that 

 yellow light has a decidedly retarding influence upon the amouut 

 of water exhaled by red and violet lights. 



Though such is the case with tlie rapidly transpiring herbaceous 

 leaves of the Lettuce, it appears to be somewhat different with 

 Palms and Box, as the following series will show ; for out of 

 ten observations on Palms on seven occasions, the loss uuder clear 

 glass was greater thau nnder violet, and on six occasions greater 

 than under red. With Lettuces the loss nnder clear glass was 

 on as many occasions greater than that under the red glass as 

 the reverse. In the case of the Box, however, the loss under 

 red and violet was always greater than under clear glass. 

 But the preponderance of red over yellow is not so pronouucea 

 as with Lettuces. 



Lettuces (third series). 

 Range of Temperature 53°-58°. 



ISro, 



E. 



Y. 



a. 



1 



I. 



II 



III 



IV 

 V 



VI 



•70 



•30 



•80 



•58 

 •29 



144 



•62 



•27 



•55 

 MO* 



•43 

 141 



•43 



•81 



•77 



1 -45 * 



•72 

 1^24 



1 



Total ... 

 Mean ... 



4-11 

 •68 



3-28 

 •65 



3^97 

 •79 



B. 



V. 



•44 

 •49 

 •69 

 •72 



•30 

 1-76 



01 



107 

 •55 

 •89 



1-83 

 •81 

 •97 



4-30 

 •71 



012 

 1-02 



•46 

 •62 

 ■62 



•70 



•59 



2-13 



5^12 



•85 



The numbers with asterisks are omitted in calculatintj tlie 

 means, as the foliage Lad become partly flaccid, and tlicy are un- 

 doubtedly too bigh. It was on these two occasions that I first 

 realized the important difference between evaporation from 



cr 



n 



dyingor dead matter and transpiration from an actively growui 

 or living plant. Subsequent experimeuts have proved that eva- 

 poration proceeds much more rapidly when life is enfeebled or 

 extinct than when the plant is alive* In the latter case this 

 purely physical process is to some extent kept in check, whue 

 transpiration, so to say, takes its place. 



