PHYSIOLOGICAL VIEWS. 
the sfed may have been placed in the ground. A botanist onco 
planted in a pot, six acorns, with the points of their embryos up- 
ward. At the end of two months, upon removing the earth, he 
found that all the radicles had made an angle, in order to reach 
downward. It is supposed that if the root met with no obstruction 
in going downward, it would always be perfectly straight. 
^^!^^^ Fig. 114 is a representation of a germina- 
^g^^^^^^^^ ting seed of the Mirabilis, (four o'clock;) it 
^^^^^^^^^^ will be seen that the radicle, a, has made 
nearly a right angle in turning downward, 
^^^^^^^^ I the plume is not developed. 
^^^^^^jy ^ If you put cotton into a tumbler of water 
Fig. 114. ™il place upon it some seeds of rye or wheat, 
mm y-Qy ^jji g^ji ^j^g fibres shooting from the 
seeds, in a perpendicular direction, downward. It is a very simple 
and interesting experiment. Some ascribe this phenomenon to the 
laws of gravitation, by which the root is attracted towards the centre 
of the earth; others say that the radicle, stimulated by moisture, ex- 
tends itself in the natural direction from which it proceeds ; while 
some imagine that the plant is endowed with a kind of instinct, 
similar to that which appears in animals from their first moments oi 
existence, leading the Uttle duck to seek the water, and the young 
bird to fly. Let us call this power by what name we will, or refer it 
to whatever secondary laws, we must ultimately attribute it to the 
will and design of Him who gave the plant its living principle. 
After the young root has made some progress, the cotyledons 
swell, and rising out of the ground, form two green leaves, called 
seed-leaves. When the plume develops its leaves, these seed-leaves 
being no longer needed wither and decay. 
You will recollect that the embryo or germ is composed of two 
principal parts, the radicle and plume. The radicle, we have just 
seen, extends itself downward. Soon after this part of the germ 
has begun its downward course, the plume, (so called from its re- 
sembling a little feather,) rises upwards, and soon becomes a tuft of 
young leaves, with which the stem, if there be one, ascends. 
" Some rye being planted in a good soil, at the end of the second 
day its radicle was discernible. At the end of twenty-four hours the 
embryo had escaped from its integument. On the second day the 
fibres of the root had augmented, but the leaves had not appeared. 
On the fourth day the first leaf began to appear above the ground, 
at which time the colour was red. On the fifth day, it had grown tr 
the length of an inch, and its colour was now green, and on the 
sixth day the second leaf had appeared."* 
Rye belongs to that class of plants whose seeds have but one 
cotyledon, and this never rises above the ground to form a seed- 
leaf. Seeds with but one cotyledon are chiefly composed of albumen, 
which performs the same office of nourishing the embryo during its 
germination, as the cotyledons of dicotyledonous plants. In some 
monocotyledons is perceived under the albumen, a part called 
vitellus, or the yolk ; this, like the albumen, is entirely converted into 
nourishment for the young plant ; it may be seen in the seeds of 
grasses, and is conspicuous in the Indian cjrn. 
* Sumner. 
Describe the experiment with acorns— Describe Fig. 114— Causes assigned for the 
downward course of the radicle— Seed leaves— Plume— Expermient with rye— Seeds 
with one cotyledon — Vitellus. 
