, and will thus be pressed down; and
they must often fall into cracks when the ground is dry, or into holes.
Even with seeds lying on the bare surface, the first developed root-hairs,
by becoming attached to stones or other objects on the surface, are able to
hold down the upper part of the radicle, whilst the tip penetrates the
ground. Sachs has shown* how well and closely root-hairs adapt themselves
by growth to the most irregular particles in the soil, and become firmly
attached to them. This attachment seems to be effected by the softening or
liquefaction of the outer surface of the wall of the hair and its
subsequent consolidation, as will be on some future occasion more fully
described. This intimate union plays an important part, according to Sachs,
in the absorption of water and of the inorganic matter dissolved in it. The
mechanical aid afforded by the root-hairs in penetrating the ground is
probably only a secondary service.
The tip of the radicle, as soon as it protrudes from the seed-coats, begins
to circumnutate, and the whole
* 'Physiologie V?g?tale,' 1868, pp.
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