113 
355. In prosecution of this idea, he procured a 
piece of tinfoil, an inch square, and with it covered 
a portion of the green leaf of a narcissus. In a few 
days, the leaf still appeared green over its whole ex- 
tent, except in the part covered by the tinfoil, which 
part was very yellow. So, likewise, if an etiolated 
leaf of the same plant was covered with a piece of 
tinfoil, and then exposed to the sun, the whole leaf 
gradually became green, except in that part covered 
by the metal * ; facts which not only demonstrate 
the direct influence of the solar rays, but likewise the 
locality of their action. 
356. In like manner too, as we have seen green 
leaves to produce oxygen gas in sunshine, after their 
separation from the stem, so do etiolated leaves be- 
come green, when placed in the same circumstances. 
M. Senebier exposed, in his window, the etiolated 
leaves of the hyacinth, to the direct rays of the sun, 
and in a few hours they became green ; but the thirt 
leaves of other plants did not exhibit, this change of 
colour, evidently because they becarffe dry before it 
could take place. When, also, etiolated plants are 
exposed in water to the sun, they become green, in 
the same manner as leaves afford oxygen gas, when 
placed in similar circumstances. He has seen the 
leaves of French beans, which sprang white out of 
the earth, become sensibly green in an hour, under 
exposure to an ardent sun t. Not only, therefore, 
do the mode and circumstances in which the green 
*Mem. Phys. Chim. vol. ii. p. 90. 
f Ibid. p. 78. 91.93, 
H 
