12 
JOUENAL OF THE EOYAL HOETICTJLTUEAL SOCIETY. 
of their carbon by the decomposition of atmospheric carbon dioxide, 
and require for their nutrition no other compound of carbon from 
without.” (Sachs’ Text-Booh (Dyer’s Trans.), p. 620.) 
ft ow in the first place one of the principal of the circumstances 
to which he certainly above alludes must be the influence of light 
on assimilation, his interpretation of which I have just endeavoured 
to refute. If that is wrong the unquestionableness of his fact dis¬ 
appears. Next I may mention another phenomenon which seems 
to me equally adverse to his views, viz., that the plants of which 
we are speaking exhale oxygen during the day and carbon during 
the night. If carbon in whatever form passes up from the root to 
the leaves during the day, and a chemical decomposition takes 
place whereby it or other ingredients are altered in its way oxygen 
must he liberated, and after being carried on with the stream of 
sap will be set free when it reaches the leaves, while the carbon 
will be used up in the plant; and this is just what takes place by 
day. But at night, when no feeding or assimilation is going on, 
no flow of matter on which chemical action can act takes place 
either, hut the carbonic acid with which the sap is charged, or 
which is one of its ingredients, escapes through the thin cuticle of 
the leaf as from a vessel left open without any interchange of oxygen 
at all. 
As to the experiments referred to by Professor Sachs, I believe that 
the principal one was made by De Saussure about the beginning of 
this century (1805), hut unhappily I have been unable to see the 
paper containing it. As recorded, Saussure’s experiment proved 
that plants in sunlight increase in their amounts of carbon, hydro¬ 
gen, and oxygen at the expense of carbonic acid and water. But 
there is no indication whether he attempted to determine whether 
the carbon was taken up by the leaves or the roots ; and as that was 
not what he was trying to find out, I am disposed to infer that no 
precautions were taken to decide that point. He seems to have 
been very careful in measuring the contents and constituents of the 
air, the plant, and the earth ; but as it is plain, from that very fact, 
that they were all three subjected to the same experiment at the 
same time, I do not imagine that the experiment could touch our 
point. The more recent experiments of Moll would require more 
space for discussion than I can give, but properly interpretated, and 
eliminating some which, I think, proceed on mistaken assump¬ 
tions, I do not consider them adverse to my views. 
It must not be inferred that I dispute altogether the possibility 
of the air supplying a portion of its carbon to the plant. Carbonic 
