stomata of the leaves.[3] We often see plants killed by the wayside dust,
and we all know that on this account it is very difficult to make a hedge
grow well by a dusty road. The dust chokes up the breathing pores of the
leaves, interfering with the action of the plant. It is suffocated.

The oxygen absorbed decomposes starch, or some other food product of the
plant, and carbonic acid gas and water are formed. It is a process of slow
combustion.[4] The energy set free is expended in growth, that is, in the
formation of new cells, and the increase in size of the old ones, and in
the various movements of the plant.

[Footnote 1: See page 13.]

[Footnote 2: This table illustrates the differences between the processes.

ASSIMILATION PROPER. RESPIRATION.

Takes place only in cells Takes place in all active cells.
containing chlorophyll.

Requires light. Can proceed in darkness.

Carbonic acid absorbed, Oxygen absorbed, carbonic
oxygen set free. acid set free.

Carbohydrates formed. Carbohydrates consumed.

Energy of motion becomes Energy of position becomes
energy of position. energy of motion.