76 VEGETABLE RESPIRATION. 
its watery part by exhalation or evaporation, this passing 
into the atmosphere when it comes into contact with 
This takes place principally under the influence of light a 
heat. Hot and dry weather greatly facilitates this opel 
tion, as Hales ascertained by experiments on the Suntl 
(Helianthus annuus), which was found in such weather 
transpire thirty ounces daily, being one-half more than 
average quantity. The Cornus mascula, or Cornelian Ch 
perhaps exceeds all other plants in the quantity o 
which it evaporates daily, amounting to nearly twice 
weight of the whole shrub. The watery part of the 
having performed its office of dissolving the solid matter 
cessary for the nutrition of the plant, thus rendering it fit 
be absorbed by the spongioles, is discharged Jas of no 
ther use. 
VEGETABLE RESPIRATION. 
267. An important operation, it is supposed, is cal 
by the leaves when under the influence of light. 
hale oxygen gas, derived from the carbonic acid in t 
mosphere, and from that conveyed to them in the sap. 
carbon is retained, being an important element in the 
position of vegetables. Light, then, it is generally be 
causes the accumulation of carbon, and the expulsion 0 of 
268. Dating the absence of light, in the night-time, 
very different process is carried on: the leaves absorb: 
gen and give out carbonic acid. 
269. The action of the leaves of plants on the atmo 
is a subject which is still involved in considerable ob 
‘The experiments of Priestley, who discovered that 
exert an action on the atmosphere, were supposed | 
_ that the general effect of vegetable respiration 
‘a dition of oxygen to the atmosphere. » abies 0° 
: Mr. Daniel Elis was of opinion that 
