The reason why : $b a careful collection of many hundreds of reasons for things which, though generally believed, are imperfectly understood. A book of condensed scientific knowledge for the million
John Stuart Mill · en
1151. _Of what do vegetable structures consist?_
Of _membranes_, or thin tissues, which, being variously arranged, form
cells, tubes, air passages, &c. Of _fibres_, which form a stronger
kind of membrane, and which is variously applied to the production of
the organs of the plants. And of _organs_, formed by those elementary
substances, by which the plants absorb, secrete, and grow, and fulfil
the conditions of their existence.
1152. _Why are seeds generally enveloped in hard cases?_
Because the covering of the seed, like the shell of an egg, is designed
_to preserve the germ_ within from the influence of external agencies,
until the time for development has arrived, and the conditions of
germination are fulfilled.
1153. _Why does a seed throw out a root, before it forms a leaf?_
Because moisture, which the root absorbs from the earth, is necessary
to enable the germ _to use the nutrition which the seed itself
contains_, and out of which the leaf must be eliminated. Moisture forms
a kind of gluten, in which the starch of the seed is dissolved, and
converted into sugar, the sugar into carbonaceous sap, and the sap into
cellular tissue and woody fibre, as the leaves present themselves to
the influence of the air and light.
1154. _Why does a plant grow?_
Because, as soon as membranes and vessels are organised in the young
germ, the nutritive fluid, formed by its first organs, _begins to move
through the fine structures_, and from that time the plant commences
to incorporate with its own substance the elements with which it is
surrounded, that are suitable to its development.
[Verse: "Can the rush grow up without mire? can the flag grow
without water? Whilst it is yet in his greenness, and not cut down, it
withereth before any other herb."--JOB VIII.]
CHAPTER LIX.
1155. _Why, if we break the stem of a hyacinth, do we see a glutinous
fluid exude?_
Because, by breaking the stem, we rupture the vessels of the plant, and
cause the nutritive fluid to escape. The sap of the plant is _analogous
to the blood of man_, and the vessels, to the arteries and veins of the
animal body.
1156. _Why, if we split the petal of a tulip, do we see cells
containing matter of various colours?_
Because, by splitting the petal of the flower, we disclose the anatomy
of its structure, and bring to view those cells, or organs, of the
vegetable body, by which _the different colouring matters are secreted_.
1157. _Why, if we break a pea-shell across, do we discover a
transparent membrane which may be removed from the green cells
underneath?_
Because we separate from the cellular, or fleshy part of the shell, the
membrane, _which forms the epidermis_, and answers to the skin of the
animal body.
1158. _Why, if we cut through a cabbage stump, do we find an outer coat
of woody fibre, and an inner substance of cellular matter?_