240 
BOUSSINGAULT’S RESEARCHES ON THE 
ACTION, OF FOLIAGE 
full abstract of the first part of these investigations 
communicated to the French Academy of Sciences, 
is given in the Comptes Rendus, vol |x., No. 18 (May, 
1865). Theodore Saussure had long ago ascertained that, 
while plants prosper and decompose carbonic acid gas in 
an atmosphere containing as much as one-twelfth or even 
one-eighth part of that gas, they promptly perish in un- 
mixed carbonic acid, apparently without decomposing any 
of it. Boussingault made his experiments in a better form 
upon leaves only, avoiding all complication of the action 
of the roots or other parts of the plant. His results are:— 
1. That leaves exposed to sunshine in pure carbonic 
acid do not decompose this gas at all, or only with extreme 
slowness. 
2. But in a mixture with atmospheric air, they decom- 
pose carbonic acid rapidly. The oxygen of the atmo- 
spheric air, however, appears to play no part. 
2. Leaves decompose carbonic acid in sunshine as 
readily when this gas is mixed with nitrogen or with 
hydrogen. 
Although this decomposition of carbonic acid by green 
foliage must be a case of dis-sociation,—a separation of 
carbon from oxygen,—yet Boussingault recognises an 
analogy here with an opposite phenomenon—viz., with 
the slow combustion of phosphorus at the ordinary tempe- 
rature. Phosphorus in pure oxygen emits no light, does 
not sensibly undergo combustion, but does so in a mixture 
of oxygen with atmospheric air, or with nitrogen, hydrogen, 
or carbonic acid. The analogy may even be carried 
further ; for, while a stick of phosphorus is not phospho- — 
rescent in pure oxygen at ordinary or increased pressure, 
it becomes so in rarified oxygen. And Boussingault 
equally ascertained that leaves which exerted no sensible 
action upon pure carbonic acid at ordinary pressure, 
decomposed it, with the liberation of oxygen gas, under 
diminished pressure: that is, rarefaction and mixture with 
an inert gas act alike in mechanically separating the 
atoms, whether of carbonic acid as in the one case, or of 
oxygen as in the other, so as to determine the action 
either of combination or of dissociation. 
