294 PRINCIPLES OF BOTANY, ETC. 
wise germinate sooner when stimulated with this 
gas. Mr Barton however discovered another great 
stimulus of plants, on which philosophers should 
make still further experiments. He found that in 
water in which camphor was diffused, a decayed 
twig rapidly recovered, which did not happen when 
it was placed in common water. A decayed branch 
of Liriodendron tulipifera and a withered’ flower of 
the yellow Iris recovered in it and remained long 
fresh. I myself tried this with a branch of Silene 
pendula, the flowers of which were quite shrivelled ; 
4m an hour’s time I found the petals again perfectly 
expanded, as if just evolved. Is it the hydrogen of 
the Camphor which stimulates the vegetable fibre to 
such a degree, as to produce this phenomenon? or 
is it a consequence of the composition of the cam- 
phor, the carbon being mixed with the hydrogen in 
such a proportion which alone can act as a stimulus 
on plants? This remains to be determined. 
Light likewise is a very powerful stimulus of the 
vegetable fibre. Every body knows that hot-house 
plants incline their stalks and leaves always towards 
the windows. A plant which has been confined for 
days in a dark room will, as soon as some light is 
admitted, however small the aperture be through 
which it passes, bend its stalks towards the light. 
‘Who does not know, that the species of Lupinus, 
especially Lupinus /ueus, turn in the open air their 
leaves and stalks towards the sun, and follow its 
course in so steady a manner, as to enable us to spe- 
' ify the hour of the day from their direction ? 
abe aly Barton 
