71 



Insolation and transpiration {or kidncii beans at Montsouris. 



Date, 1877. 



July 10. 

 17 

 18. 

 19. 

 20 

 21 



Weight 

 of tran- 

 spired 

 water. 



Weight of tran- 

 spired water 

 divided by- 



Moan 

 actino- 



Grams. 

 0.686 

 0.422 

 0.727 

 0.543 

 0.577 

 1.127 

 1.608 

 1.204 



degrees. 



1.16 

 1.36 

 1.21 



1.56 

 1.24 



1.81 

 1.88 



July 24 

 25 



26 

 27 

 28 

 29 

 30 

 31 



Weight 

 of tran- 

 spired 

 water. 



Weight of tran- 

 spired water 

 divided hy— 



Mean 

 actino- 



degrees. 



Cframs. 

 0.706 

 1.300 

 0.991 

 1.255 

 1.426 

 1.277 

 2.167 

 2.710 



3.8 

 7.1 

 5.3 

 6.7 

 7.8 

 5.9 

 7.6 

 8.4 



2.00 

 2.17 

 1.92 

 2.46 

 2.64 

 2.97 

 3.55 

 3.15 



The figures in the above table are influenced by the quantity of 

 moisture in the soil; therefore Marie Davy occasionally omitted the 

 evening watering, and the transpiration for the day after such omis- 

 sion was smaller. In general, Marie Davy concludes that the relation 

 between transpiration and temperature is very variable from day to 

 day, while that between transpiration and radiation is very regular, 

 u regularity that would very probably be heightened if the cloudiness 

 and the evaporating power of the wind, as depending on its dryness 

 and velocity, had been considered. The belief is that sunshine excites 

 the contraction of the stomata of the leaves and thus stimulates tran- 

 spiration; but the stomata can not exude water to a greater extent 

 than as supplied by the roots; therefore the transpiration is limited 

 by the humidity of the soil adjacent to the roots. Thus on the 30th 

 the radiation averaged 45.5 actinometric degrees, and the plant tran- 

 spired 2.167 grams of water; on the 31st the radiation was 64.1 and 

 the transpiration correspondingly increased to 2.710 grams; but on 

 this day the reserve moisture in the soil was drawn upon very heavily, 

 and in the evening the leaves of the plant were flabby and drooping 

 and evidently wilting for the want of moisture. 



The result's by Deherain at temperatures of 15° C. and 0° C. and 

 those by Marie Davy seem to demonstrate satisfactorily the slight 

 influence of the temperature of the air as such ui:)on transpiration. 



Daubeny (1836), Deherain, and Wiesner have studie<l the effect of 

 radiation in different parts of the spectrum, and their work shows 

 that the radiations that are absorbed by chloroi)hyl, the so-called 

 chlorophyl-absorption bands, are those that are efficient in stimulat- 

 ing transpiration; also that xanthoi)hyl acts similarly, but weaker 

 than chlorophyl; that the violet and ultraviolet have no appreciable 

 influence: that the ultrared rays liavc an api)re<'iable action, but 

 feebler than the visible ravs between the red and blue, notwithstand- 



