unknown. Thus the invention of the microscope from a simple
lens magnifying 3 or 4 times into progress up to 1500 diameters has
given birth to new sciences. But still higher magnification is demanded
in unravelling the mystery of movements associated with the simplest
type of life as seen in plants. Greatest potentiality in life is often
latent; the gigantic banian tree grows out of a thing which is smaller
than the mustard seed. Within the seed-coat the dormant life remains in
safety, protected from dangers outside. The seeds may thus be subjected
without harm to cold so intense as will freeze mercury into solid and
air into liquid. Winds and hurricanes scatter the seed of life and the
cocoa-nut rides the tumultuous waves till anchored safe in an island
yet to be inhabited. In due season there begins a series of most
astonishing transformations; the latent life wakens, and the seedling
begins to grow. The root turns downwards and the shoot upwards.
Underground, the root winds its way round stones and obstacles towards
moist places. Above ground the stem bends as if in search of light.
Tendrils twine about a support. These visible movements are striking
enough, but within the unruffled exterior of the plant body there are
others, energetic and incessant, which escape our scrutiny. The bending
of a growing organ towards or away from stimulus must be due to unequal
growth on two sides of the organ, a retardation of growth on the
proximal or acceleration on the distant sides. Various theories have
been advanced which have proved inadequate. For the identical stimulus
of gravity produces one kind of curvature in the root and the very
opposite in the shoot. The possibility of direct experimental
investigation has been frustrated by the excessive slow rate of growth
rendering accurate measurement impossible.

THE SLOWNESS OF GROWTH

The movement of growth is two thousand times less rapid than the place
of the proverbially slow-footed snail. Taking the average annual growth
in height of a tree to be 5 ft., it will take a tree a thousand years
to cover a distance of a mile. We take a piece of 2 ft. in the course of
half a second, during the interval plant grows through a length of
1,100,000 part of an inch or half the length of a wave of light. For
investigation on the effect of external conditions on growth we have to
measure even a fraction of that excessively small length.

The peasant has eagerly watched the growth of