I. Origin of Cultivated Plants.]

This lesson may be followed by a talk on food and the various plants used
for food.[2]

[Footnote 2: The Flour Mills of Minneapolis: Century Magazine, May, 1886.
Maize: Popular Science News, Nov. and Dec., 1888.]


2. _Clothing_.--Plants are used for clothing. Of the four great clothing
materials, cotton, linen, silk, and woollen, the first two are of
vegetable, the last two of animal origin. Cotton is made from the hairs of
the seed of the cotton plant.[1] Linen is made of the inner fibre of
the bark of the flax plant. It has been cultivated from the earliest
historical times.

[Footnote 1: Reader in Botany. II. The Cotton Plant.]


3. _Purification of the Air_.--The following questions and experiments are
intended to show the pupils, first, that we live in an atmosphere, the
presence of which is necessary to support life and combustion (1) and (2);
secondly, that this atmosphere is deprived of its power to support life
and combustion by the actions of combustion (2), and of respiration (3);
thirdly, that this power is restored to the air by the action of plants
(4).

We have the air about us everywhere. A so-called empty vessel is one
where the contents are invisible. The following experiment is a good
illustration of this.