V. The Influence of Light upon tbe Growth of Leaves. 
117 
and bearing many other branches vvhich were well supplied with leaves. 
Such a branch was secured in a glass receiver filled wilh air which had 
previously passed Ihrough a solulion of caustic polash. Under these cir- 
cumstances the leaves borne by this branch were by no means arrested 
in their development. On the contrary, the more favourable temperalure 
within the receiver so assisted their growth, that, at the end of the expe- 
riment, they were more fully developed than those which had grovvn in 
the open air. From these observations Corenwixder concludes that leaves 
are able to assimilate not only the carbonic acid which they oblain 
directly from the air, but also the carbonic acid which reaches them 
from the tissues of the plant. In support of this view he quoles an 
experiment of De Saussure, in which a leafy branch, still in connection 
"ith the tree, was enclosed in a receiver full of air containing no car¬ 
bonic acid. At the end of the experiment it was found that the percen- 
tage of oxygen in the air within the receiver was perceptibly higher tban 
in ordinary air. 
These facls, however, cannot be regarded as affording sufficient evi- 
dence to substantiate the Statement that leaves do actually assimilate the 
carbonic acid which is evolved by their own tissues or which is obtained 
from other parls of the plant. The experiments of Moll : ) tend to prove 
that the contrary is the case. He finds that neither a leaf nor a pari of 
a leaf, when in an atmosphere containing no C0 2 , can form starch in 
visible quantity, although other parts of the plant, subaerial or subter- 
rauean, are surrouuded by C0 2 in abundance. It is true that the starch, 
which makes its appearance in chlorophyll-grains, is only the excess of the 
producls of assimilalion 1 2 ), and it may perhaps be assumed that, in Moll’s 
experiments, assimilation actually occurred, although it never produced such 
a quantity of carbohydrales, in excess of the demands of the growing 
parts of the plant, that a deposition of starch in the chlorophyll-grains of 
the leaves could take place. Such an assumption is clearly improbable, 
for the amounl of C0 2 supplied to those parts of the plant which were 
not under observaliou, was so large that, had it penetrated Ihrough the 
tissues to the chlorophyll-grains of the leaf which was in an atmosphere 
derived of C0 2 , it would most probably have given rise to the formation 
of starch within them. It is probably more correct to assume that the 
growth of Ihe leaves in air deprived of its carbonic acid went on at the 
expense of nutritious substances conveyed from other parls of the plant 
to the growing cells, just in the same way as the growth of the slem is 
supported by material drawn either from the organs, which are the store- 
houses, or from those which are the factories of the plaslic substances. 
1) Ueber den Ursprung des Kohlenstoffs der Pflanzen. (Landw. Jahrb. 1877.) 
2) Godlewski in Arb. des bot. Inst, in Würzburg. Heft III, p. 343. 
