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.
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