, small, hard
lumps begin to appear under the skin of the stem of the broken seedling
Bean. These gradually increase in size until, finally, they rupture the
skin and appear as rootlets. Roots are always thus formed under the outer
tissues of the stem from which they spring, or the root from which they
branch. In the Bean, the roots are in four long rows, quartering the stem.
This is because they are formed in front of the woody bundles of the stem,
which in the seedling Bean are four. In the Sunflower the roots divide the
circumference into six parts. In some of my cuttings of Beans, the stem
cracked in four long lines before the roots had really formed, showing the
parenchyma in small hillocks, so to speak. In these the gradual formation
of the root-cap could be watched throughout, with merely a small lens. I
do not know a better way to impress the nature of the root on the pupil's
mind. These forming roots might also be marked very early, and so be shown
to carry onward their root-cap on the growing-point.

4. _Root-hairs_. These are outgrowths of the epidermis, or skin of the
root, and increase its absorbing power. In most plants they cannot be seen
without the aid of a microscope. Indian Corn and Oats, however, show them
very beautifully, and the scholars have already noticed them in their
seedlings. They are best seen in the seedlings grown on damp sponge. In
those grown in sand, they become so firmly united to the particles of
soil, that they cannot be separated, without tearing the hairs away from
the plant. This will suggest the reason why plants suffer so much from
careless transplanting.

The root-hairs have the power of dissolving mineral matters in the soil
by the action of an acid which they give out. They then absorb these
solutions for the nourishment of the plant. The acid given out was first
thought to be carbonic acid, but now it is supposed by some experimenters
to be acetic acid, by others to vary according to the plant and the time.
The action can be shown by the following experiment, suggested by Sachs.

[Illustration: Fig. 12. I. Seedling of _Sinapis alba_ showing root-hairs.
II. Same, showing how fine particles of sand cling to the root-hairs.
(Sachs.)]

Cover a piece of polished marble with moist sawdust, and plant some seeds
upon it. When the seedlings are somewhat grown, remove the sawdust, and
the rootlets will be found to have left their autographs behind. Wherever
the roots, with thei