The reddening of our sundew patch has brought back to my mind various
sundew experiments, carried on long since, with all the zeal of youth
and enthusiasm. In this, as in every other walk of biology, the
investigators of those days, amateur and scientist alike, followed with
docility in the wake of their master. Darwin played the tune, and all
the rest of us, great and small, danced to his piping.
To the best of my recollection my own investigations were chiefly
carried on standing stork fashion upon a tussock, surrounded by an inky
opacity, which threatened to draw the investigator downwards with a
clutch, more tenacious and formidable than that of any sundew. To the
faithful Irish botanist the poverty of the Flora of Ireland as compared
with that of Great Britain has always been a serious humiliation. In
this respect these Droseraceæ form an exception. Of the few British
species all, I think, are to be found upon the bogs of the West of
Ireland, the largest of them--appropriately called anglica--being much
commoner in Ireland than elsewhere in these islands.
A very slight acquaintance with their habits could hardly fail, I think,
to convince even the most sceptical that their roots are mainly employed
as anchors, and water-pipes, while for a supply of that nitrogen which
every plant requires they are chiefly, if not exclusively, dependent
upon insects. Of these the two lesser species would appear to content
themselves with the smallest of Diptera and Lepidoptera, whereas anglica
will occasionally tackle larger prey, and I have myself seen it with a
good-sized moth (a noctua) attached to and nearly covering the entire
disk, the long tentacle-like hairs being closely inflected over the
victim, whose struggles are soon put an end to, once the sticky
secretion exuding from the hairs closes above the trachea. When the leaf
re-opens nearly the whole of the insect (be it fly, moth or beetle) will
be found to have disappeared, even the wings being reduced to a few
glittering fragments. No animal substance in fact comes amiss; fragments
of bone, hide, meat-fibrine, and even, according to one authority, tooth
enamel, softening, and in time dissolving under the powerful solvent
secreted by the glands. Whether the Droseraceæ have the power of
attracting their prey, or must wait until chance sends it within their
clutches, seems undecided. In the case of a little Portuguese relative,
one Drosophylum lusitanicum (growing, unlike other members of the
family, upon _dry_ hills in the neighbourhood of Oporto) such a power
appears undoubtedly to exist, the people of the neighbourhood using it
as a flycatcher, and hanging it upon their walls for that express
purpose.
This meat-eating habit or instinct (whichever we may agree to call it)
is shared to a greater or less extent by all the Droseraceæ, such as the
Venus’s fly-trap, the Byblis gigantea of Australia, and a small but
curious aquatic cousin, known to botanists by the formidable name of
Aldrovanda vesiculosa, whose tiny leaves have the power of shutting
vice-like over every unfortunate insect which approaches them, and which
thus finds itself enclosed in a floating prison. If eminently
characteristic of them, this carnivorousness is by no means confined
however to the sundews, and their allies. If anything the Pinguiculas,
for instance, rather exceed them in voracity. Few plants are at once so
beautiful, and so interesting from the problems to which their
distribution gives rise, as is the great Irish butterwort--Pinguicula
grandiflora. Unknown to England and Scotland; unknown to the whole north
of Europe; unknown even to the rest of Ireland; its viscid green
rosettes may be seen on most of the lowlands of Kerry, and upon many of
the bogs of south Cork. For nine months of the year that is all that
there is to see. In June a flower-stalk rises out of the centre of the
rosette, crowned with a pendulous bell of the most pellucid, the most
ethereal shade of violet. Happily for the susceptibilities of the
investigator this is not the flesh-eating portion of the plant, that
office being strictly confined to the leaves. Stooping down and
examining these leaves we find that, whereas some are flat, others are
slightly dog-eared along the edges. If further we unroll a few of the
dog-ears we discover the remains, not of one alone, but often of a dozen
unfortunate flies and midges, in all stages of assimilation; some
already half-digested, others still alive, and struggling to escape from
their glutinous prison. If further we place a fragment of bone, of meat,
or indeed of any nitrogenous substance, upon the edge of one of the
fully expanded leaves, we shall find that little by little the leaf
begins curling upwards, until the two edges approach, and then join.
Finally the morsel is lost to sight, becoming entirely immersed in its
bath of secretion, where it remains until all its nutritive parts are
absorbed.
Viscous as the whole surface of the leaf is, it does not seem as if this
process of digestion was carried on with the same rapidity in the centre
as at the sides, and, as there are in this case no long hairs to act as
locomotive organs, it often happens that one may see flies and other
small insects lying partially dried up and useless in the centre of the
leaf. In one respect this viscidity appears at first sight to be
inconvenient, the entire surface of the leaf being often covered with
twigs, leaves, particles of boggy fibre, and such-like matters, which
the plant has apparently no power of getting rid of. In the end this may
prove however to be an advantage rather than otherwise, since it has
been ascertained that the Pinguiculas feed, not alone on animal, but
also on vegetable substances; the extreme stickiness of the leaves
causes them moreover to act as a chevaux-de-frise, thus hindering small
but industrious ants from making their way up the flower-stalks to the
corolla.
Yet another little group of bog-plants, namely, the Utricularias, or
bladderworts, are meat eaters. In their case the fly-catching apparatus
is situated, not in the leaves, but in certain small attached
air-bladders, which are constructed almost exactly upon the principle of
an eel-trap, and which, if opened, may generally be found to contain
flies. Thus we see how discovery may be anticipated, and how one of
man’s most boasted attributes--that of the Destroyer--may be wrested
from him by a miserable little green bog-weed! Before the first Celtic
hunter flung spear at wolf or stag; before the Firbolgs, or the
Tuatha-da-Daanans--cunning workers and craftsmen--had set up any gins
or traps in the wilderness; before the first monk or abbot had arranged
ingeniously devised weirs, wherein the salmon--seemingly by
miracle--rang a bell to announce its own arrival; before any of these
things had been done, or thought of, little Utricularia minor and little
Utricularia intermedia had set up their own primitive green eel-traps in
the yet unvisited wastes of Iar-Connaught.