ome special function to perform. The
roots absorb food and drink from the soil. The leaves breathe in
carbonic acid from the air and transform it into the living substance of
the plant. Every plant has, therefore, an anatomical structure, its
parts and tissues visible to the naked eye.

[Sidenote: What the Microscope Shows]

Put one of these tissues under a microscope and you will find that it
consists of a _honeycomb of small compartments or units_. These
compartments are called "cells," and the structure of all plant tissues
is described as "cellular." Wherever you may look in any plant, you will
find these cells making up its tissues. The activity of any part or
tissue of the plant, and consequently all of the activities of the plant
as a whole, are but the combined and co-operating activities of the
various individual cells of which the tissues are composed. _The living
cell, therefore, is at the basis of all plant life._

[Sidenote: The Little Universe Beyond]

In the same way, if you turn to the structure of any animal, you will
find that it is composed of parts or organs made up of different kinds
of tissues, and these tissues examined under a microscope will disclose
a cellular structure similar to that exhibited by the plant.

_Look where you will among living things, plant or animal, you will find
that all are mere assemblages of cellular tissues._

Extend your investigation further, and examine into forms of life so
minute that they can be seen only with the most powerful microscope and
you will come upon a _whole universe of tiny creatures consisting of a
single cell_.

[Sidenote: The Unit of Life]

Indeed, it is a demonstrable fact that these tiny units of life
consisting of but a single cell are far more numerous than the forms of
life visible to the naked eye. You will have some idea of their size and
number when we tell you that millions may live and die and reproduce
their kind in a single thimbleful of earth.

_Every plant, then, or every animal, whatever its species, however
simple or complicated its structure, is in the last analysis either a
single cell or a confederated group of cells._

All life, whether it be the life of a single cell or of an unorganized
group of cells or of a republic of cells, has as its basis the life of
the cell.

For all the animate world, two great principles stand established.
First, that _every living organism_, plant or animal, big or little,
develops from