17 
A. E. GIBBS—SEEDS AND ERTJITS. 
moisture, heat, and air. It is not absolutely essential that the seed 
should be planted in the ground. A very old-fashioned experiment 
will prove that. It is that of the cress seed growing upon a piece 
of flannel, and here there is certainly no soil present. The seed is 
merely placed upon a piece of damp flannel, put in a warm place, 
and it germinates. The young cress plants simply live upon 
themselves, consuming the food stored up in their own tissues. 
When that is exhausted the cress dies, for it can get no nutriment 
from the flannel, and not a sufficient amount from the water to 
keep it alive. Let the conditions of heat, moisture, and air be 
applied to a seed—take a pea-seed for instance—and it will begin 
to swell, and the young plant will burst its envelopes and grow. 
If we examine the pea-seed carefully we shall find that it really 
consists of two parts. There is a living part, a small object which 
is the embryo or young plant, and the remainder consists of the 
seed coverings, and in some seeds a store of nutrient matter called 
albumen, on which the young plant is fed until it is able to strike 
out for itself and get its own living. The seed of the pea contains 
no albumen, the seed of the wheat on the contrary is made up for 
the most part of it. The pea starts life on the nutriment contained 
in the tissues of the seed-leaves. 
The laws which regulate the direction of growth are very inter¬ 
esting, but the subject is a complex one. 
All good seeds contain an embryo, which as we have seen will 
become the future plant. This consists of two parts, the radicle 
from which the young root is developed, and the plumule which be¬ 
comes the stem. The former invariably grows downwards into the 
ground, and the latter upwards towards the light, and they do this 
in obedience to fixed laws. Whichever way a seed may be turned, 
the direction of growth is always the same. The root obeys a 
force acting in the same direction as gravitation, that of geo- 
tropism as it is called, and therefore commences to descend; but 
another force also comes into play, called apogeotropism or a 
growing away from the centre of gravity, both these forces being 
at work at the same time, one pulling one way and one another. 
Darwin, in his most interesting book on ‘ The Movements of 
Plants,’ has shown that if a number of seeds be thrown on the sur¬ 
face of the ground under conditions suitable to germination, the 
young root appears and through the combined action of these forces 
commences to circumnutate, or bow around in a spiral manner. By 
this means it gradually bends towards the ground, and at length 
pierces the soil. Then it gives out a number of very fine root- 
hairs by which it is anchored in position, or the downward thrust 
of the root would force the young plant out of the ground. The 
tip of the root goes on growing and circumnutating, and when it 
comes into contact with any hard substance it bends away from it. 
So sensitive is it that if it becomes aware of the presence of moisture 
it will grow towards it. Many experiments were undertaken by 
Mr. Darwin to show the extreme sensitiveness of the tip of the 
growing radicle, particulars of which will be found in his book 
2 
VOL. VI. —PART I. 
