We pencil a few passages, at random, from Part 14 of _Knowledge for the
People_--(Botany, concluded.)
_Why does snow, when in contact with leaves and stems, melt more speedily
than when lodged upon dead substances?_
Because of the internal heat of the plants, heat being a production of the
vegetable as well as animal body, though in a much lower degree in the
former than the latter. Mr. Hunter appears to have detected this heat by a
thermometer applied in frosty weather to the internal parts of vegetables
newly opened. It is evident that a certain appropriate portion of heat is
a necessary stimulus to the constitution of every plant, without which its
living principle is destroyed.--_Smith_.
_Why is fructification so important to plants?_
Because it continues them by seeds, and, according to Sir James Smith,
"all other modes of propagation are but the extension of an individual,
and, sooner or later, terminate in its total extinction." Dr. Drummond is
of a contrary opinion, and quotes the following fact:--"In South America
there is a species of bamboo which forms forests in the marshes of many
leagues in extent, and yet Mutis, who botanized for nearly twenty
years in the parts where it grows, was never able to detect the
fructifications."--_Humboldt_.
The produce of vegetable seeds in a hundred-fold degree is common, and
many trees and shrubs bring forth their fruit by thousands. A single plant
of the poppy will produce above 30,000 seeds; and, of tobacco, above
40,000; and Buffon remarks, that from the seeds of a single elm-tree, one
hundred thousand young elms may be raised from the product of one year.
Some ferns, it is said, produce their seeds by millions.
_Why should seeds be uniformly kept dry before sown?_
Because the least damp will cause an attempt at vegetation, when the seeds
necessarily die, as the process cannot, as they are situated, go on.
_Why, in summer, is continued watering required to newly sown seeds?_
Because, if the soil is only moistened at the time of sowing, it induces
the projection of the radicle, or first root, which, in very parching
weather, and in clayey cutting soil, withers away, and the crop is
consequently lost, for want of a continued supply of moisture.
_Why is selection important for procuring abundance of genuine seeds?_
Because we may then choose the most vigorous plants, which naturally prove
of greater fecundity. Thus, in 1823, Mr. Shirreff marked one vigorous
wheat plant, near the centre of a field, which produced him 2,473 grains.
These were dibbled in the autumn of the same year, the produce sown
broadcast the second and third years, and the fourth harvest produced
forty quarters of sound grain. A fine purple-topped Swedish turnip
produced 100,296 grains, which was seed enough for five imperial acres,
and thus, in three years, one turnip would produce seed enough for Great
Britain for a year.--_Quarterly Journal of Agriculture._
_Why are winds the great agents by which seeds are diffused?_
Because seeds are, as it were, provided with various wings for seizing on
the breeze. The thistle and dandelion are familiar examples of this mode
of dissemination. "How little," Sir J.E. Smith observes, "are children
aware, as they blow away the seeds of dandelion, or stick burs in sport
upon each other's clothes, that they are fulfilling one of the great ends
of nature." Dr. Woodward calculates, that one seed of the common spear
thistle will produce "at the first crop, twenty-four thousand, and
consequently five hundred and twenty-six millions of seeds, at the second."
Some plants discharge their seeds. Thus, a certain fungus has the property
of ejecting its seeds with great force and rapidity, and with a loud
cracking noise, and yet it is no bigger than a pin's head!
_Why is a milky fluid found in the cocoa-nut?_
Because in this case, as well as in a few others, all the fluids destined
to nourish the embryo of the fruit does not harden, whence a greater or
less quantity of this kind of mild emulsion is contained within the kernel.
_Why are certain eatable roots unfit for the table when the plants have
flowered?_
Because the mucus or proper juice in the tubular cells being appropriated
for perfecting the flower stem, the flower, and the fruit, is absorbed as
the fructification of the stem advances; and, as these are perfected, the
cells are emptied, and their sides become ligneous.
_Why is the Jerusalem Artichoke so called?_
Because of its corruption from its Italian name, _Girasole Articiocco_,
sunflower artichoke, as the plant was first brought from Peru to Italy,
and thence propagated throughout Europe.--_Smith._
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