All of the species are remarkably similar in habits, capturing insects,
and digesting and absorbing the soft parts, a circumstance which
explains how these plants can flourish in an extremely poor soil where
mosses, which depend almost entirely upon the atmosphere for their
nourishment, only can live. Although the leaves of the Droseras at
a hasty glance do not appear green, owing to the purple color of the
tentacles, yet the superior and inferior surfaces of the blade, the
stalks of the central tentacles, and the petioles contain chlorophyll,
rendering the best of evidence that the plants obtain and assimilate
carbon dioxide from the air. But when the poverty of the soil where
these plants grow is considered, it is at once apparent that their
supply of nitrogen would be exceedingly small, or quite deficient,
unless they had the power of obtaining it from some other source. From
captured insects this important element is largely obtained, and thus
we are prepared to understand how it is that their roots, which consist
of only two or three slightly divided branches, from one-half to one
inch in length, and furnished with absorbent hairs, are so poorly
developed. From what has been stated it would seem that the roots but
serve to imbibe water, but there is no doubt that nutritious matters
would also be absorbed were they present in the soil.
With the edges of its leaves curled so as to form a temporary stomach,
and with the glands of its closely-inflected tentacles pouring forth
their truly acid secretion, which dissolves animal matters that are
subsequently absorbed, Drosera may be said to feed like an animal. But,
unlike an animal, it drinks by means of its roots, and largely, too,
for it would not be able to supply its glands with the necessary viscid
fluid. The amount needed is by no means an inconsiderable quantity, as
two hundred and seventy drops may sometimes be exposed during a whole
day to a glaring sun. Such a profuse exudation implies preparations for
hosts of insect visitors. In this Drosera has not miscalculated. Its
bright pink blossoms and brilliant, glistening dew lure vast numbers of
the smaller kinds, and the larger ones, too, to certain death. But the
wholesale destruction of life that goes on is much in excess of what
the plant requires for food. While the smaller flies remain adherent
to the leaves, affording them the needed aliment, the larger insects,
after death, fall around the roots, where they decay and fertilize
the soil with nitrogen, which doubtless through the proper channels
makes its way into the body of the plant, thus helping to give it
tone and vigor. There are times when these plants work better than at
others, but whether this is caused by the electrical condition of the
atmosphere, or the amount of its contained moisture, is a question
which science has not positively determined.
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