om methylic aldehyde,
and, on the other, we find this glucose in leaves by using Fehling's
solution.

The glucose formed, it is admissible that a new polymerization with
elimination of water produces starch. The latter, in fact, through the
action of an acid, is capable of regenerating glucose.

It may, therefore, be supposed that the decomposition of carbonic acid
by leaves brings about the formation of starch through the following
transformations: (1) The decomposition of the carbonic acid with
emission of oxygen and production of methylic aldehyde; (2)
polymerization of methylic aldehyde and formation of glucose; (3)
combination of several molecules of glucose with elimination of water;
formation of starch.

Starch is thus the first stable product of chlorophylian activity. Is
there, in fact, starch in leaves? It is easy to reveal its presence by
the blue coloration that it assumes in contact with iodine in a leaf
bleached by boiling alcohol.

Mr. Deherain has devised a nice method of demonstrating that this
formation of starch, and consequently the decomposition of carbonic
acid, can occur only under the influence of sunlight. He pointed it
out to us in his course of lectures at the School of Grignon, and
asked us to repeat the experiment. We succeeded, and now make the
_modus operandi_ known to our readers.

The leaf that gave the best result was that of the _Aristolochia
Sipho_. The leaf, adherent to the plant, is entirely inclosed between
two pieces of perfectly opaque black paper. That which corresponds to
the upper surface of the limb bears cut-out characters, which are here
the initials of Mr. Deherain. The two screens are fastened to the leaf
by means of a mucilage of gum arabic that will easily cede to the
action of warm water at the end of the experiment.

The exposure is made in the morning, before sunrise. At this moment,
the leaf contains no starch; that which was formed during the
preceding day has emigrated during the night toward the interior of
the plant.

After a few hours of a good insolation, the leaf is picked off. Then
the gum which holds the papers together is dissolved by immersion in
warm water. The decolorizing is easily effected through boiling
alcohol, which dissolves the chlorophyl and leaves the leaf slightly
yellowish and perfectly translucent.

There is nothing more to do then but dip the leaf in tincture of
iodine. If the insolation has been good, and if the screens have be