292 PRINCIPLES OF BOTANY, ETC. 
tion of water. Conferva rivu/aris, when exposed in 
a glass vessel to the rays of the sun, constantly 
evolves new shoots. ‘Trees likewise shew how be- 
neficial for them the influence of light is, as they 
all grow thicker and fuller of leaves towards the 
south. 
The same stimulus which the oxygen gas in sun- 
shine offers to the vegetable fibre, likewise produces 
in it the state of sleep. After constant application 
of stimuli, relaxation must necessarily follow, of 
which the consequence is, that in the evening the 
leaves become folded up. For the very same rea- 
son some plants fold and unfold their leaves at cer- 
tain hours. Du Hamel’s experiment, mentioned 
above, with the plant, which he put into a trunk, 
might perhaps be explained in this way. The 
leaves could not but open in the morning, after they 
had during night imbibed moisture enough to resist 
the new ule ; but how did it happen that they 
shut again in the darkness of a certain hour, when 
no light could effect the decomposition of water? 
Du Hamel did not make the experiment with suffi- 
cient accuracy, for he did not examine the state of 
the air, in which the plant in the trunk was placed. 
Had there been hydrogen gas in it, the experiment 
could be easily explained, as this gas acts in the same 
manner upon plants as light does. 
The oxygen gas, if accumulated to a great degree, 
makes leaves and all parts of vegetables pale and 
even white. ~ 
Hence it is, that plants in the dark, when the 
gas cannot be evolved by light, grow whitish. 
Mr 
