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.
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