132 
fcffects ; and such leaves, therefore, like green infu* 
sions which have been exposed to the air or mixed with 
acids, will, from a similar cause, experience a similar 
degradation of colour, arid exhibit only a white or 
yellow hue. 
383. But, farther, if carbonic acid thus supera* 
bound in etiolated leaves, and destroy their colour, 
by modifying or overpowering the action of alkaline 
matter, this etiolation must continue as long as the 
acid is thus retained ; and this must happen as long 
as the plant is kept in darkness, since little air is af- 
forded by etiolated leaves, and that little is always im- 
pure*; Hence, therefore, the etiolated state of 
plants depends immediately on a deficiency of alka- 
fine, or on a superabundance of acid matter, by 
\vhich the usual operation of the alkali is reduced or 
counteracted : but the sun's rays, by withdrawing 
and decomposing this excess of acid, enables the al- 
kali to resume its former action, and thereby to re- 
store the green colour of the leaf. This view, there- 
fore, corresponds with the local operation of light 
(355.), in the restoration of the green colour ; with 
the fact of the formation of this colour in leaves 
(356.), in which vegetation is necessarily suspended ; 
with the results of those experiments (375.), in which 
white leaves were rendered green, by immersion in 
alkaline fluids ; and also with those, in which the 
white juices of such leaves (373.) were made green, 
by the addition of alkaline matter. 
384. These views, respecting the colouration of 
* Mem. Thys. Chim. tcm. ii. p/1'55. 
