800 REV. G. HENSLOW ON TRANSPIRATION 
of light. Taking the means of the above, we have as results, 
irrespective of colour :— 
Mean loss by Mean loss in 
day. Min. Max. darkness. Min. Max. 
‘106 51 56 ‘087 52 56 
Comparing these results with the mean losses by transpiration 
irrespective of colours :— 
Mean loss by Mean loss in 
day. Min. Max. darkness. Min. Max. 
*056 50 53:3 049 53:8 57 
In both cases, as with Mushrooms, the loss is greater under 
light than in darkness ; and probably the same interpretation 
may be given here as with the former experiments. 
Again, as it was observed (on p. 294) that the transpiration of 
Mushrooms was greater than their evaporation, similarly is it with 
Seakale. In the latter case the evaporation is nearly double that 
of transpiration. So great a difference possibly depends upon the 
different natures of the cellular tissues of these two plants, though 
I confess at present to be quite unable to explain it. That there is 
some similarity, if not identity in part, between the two processes 
of transpiration and evaporation seems obvious, yet that the vitality 
of a living plant has an important modifying influence is equally 
apparent. Leclerc considers transpiration as not being due to 
light per se, but to the calorific rays which accompany it. But 
though the chlorophyll absorption-band No. I. coincides pretty 
nearly with the maximum of the calorific rays (as Langley and 
Abney have shown *), it is difficult to see in what way Leclerc 
would explain how a maximum of transpiration is obtained with 
violet light, as both Wiesner and myself have proved, and which 
we believe to be converted into heat, and thus do work. 
One great point of difference between transpiration and eva- 
poration in their final results consists in the relatively greater 
quantity of water lost, and that with a greater rapidity, by 
evaporation as compared with transpiration. Thus, for example, 
the mean loss by transpiration under all lights of a plant of 
Echeveria was ‘033 gramme per hour; while the same plant 
scalded to death evaporated :068 gr. per hour under a very 
* “The Influence of Water in the Atmosphere on the Solar Spectrum and 
Solar Temperature,” by Capt. Abney, R.E.,F.R.S.,and Col. Festing. Proc. Royal 
Soc. xxxv. p. 328 (1883). 
