pment of plant-roots is one of the highest importance
and interest, and is not so generally recognised as it ought to be.

_Natural tendency of Plant-roots to grow downwards._

It may be taken as certain that the tangled condition of plant-roots is
due to the resistance offered by the soil-particles, and that the
natural tendency of the plant-root is to grow downwards. The roots, in
short, would probably grow in as symmetrical a form as do the stalks or
branches, were it not that they are hindered from so doing by the
soil-particles. Where, then, the soil is such as to offer much
hindrance, the growth of the plant cannot but be retarded. Some
extremely interesting experiments have been performed by the eminent
German chemist Hellriegel on the influence which the closeness of the
soil-particles has on root-development. In these experiments peas and
beans were grown in moistened sawdust, more or less compactly
compressed. It was found that when the sawdust Was compressed to any
extent, plant-growth took place very slowly, or entirely ceased.

The importance of having plant-roots as widely developed in the soil as
possible, will be at once seen when we reflect that this means that the
area of soil from which the plant derives its soil-food is thereby
greatly increased. Another important consideration is, that the deeper
plant-roots can penetrate in a soil, the more able--other conditions
being equal--is the plant to withstand the action of drought, as it can
draw water for its needs from the deeper layers of the soil, long after
a plant, whose roots do not penetrate so deeply, has wilted.

_Plants require Room._

Another important bearing tillage has on plant-growth may here be
discussed. A problem of considerable difficulty is presented in the
question, How many individual plants will a certain piece of soil
support in a healthy way? For as plants require room, it is imperative
that they be not too closely crowded together.

The question resolves itself pretty much into one of quality against
quantity.

Experiments on this subject have shown that a certain area of soil is
only able to support the healthy growth of a certain number of plants.
If the limit be exceeded, the result is imperfect development.

_Number of Plants on certain Area increased by Tillage._

It is obvious, however, that the more thoroughly tilled a soil is, the
greater will be the number of plants it will be possible to grow on it.
The