(_By John Murray, Esq. F.S.A. &c._)
The secretions of trees form a curious part of their physiology, but the
influence of vegetation on the atmosphere seems to have been entirely
overlooked, at least as far as it regards its meteorology.
In the case of that curious genus of plants the Sarracèn_ia_, in
which the S. adúnca is most conspicuous, the foliaceous pouch is a mere
reservoir, or cistern, to catch and retain the falling dew or rain.
In the _N_epénthes distillatòria, or pitcher plant, the case is
different; and analysis proves it to be an evident secretion from the
plant itself, independent altogether of the fact that it is found in
the pitcher before the lid has yet opened. I may here state, _en
passant,_ that the results, I obtained from a chemical examination
of this liquid differ materially from those of Dr. Edward Turner. The
_C_órnus máscula is very remarkable for the amount of fluid matter
which evolves from its leaves, and the willow and poplar, when grouped
more especially, exhibit the phenomenon in the form of a gentle shower.
Prince Maximilian, in his _Travels in the Brazils_, informs us that
the natives in these districts are well acquainted with the peculiar
property of those hollow leaves that act as recipients of the condensed
vapours of the atmosphere; and, doubtless, these are sources where many
tropical animals, as well as the wandering savage, sate their thirst
"in a weary land." The Tillánds_ia_ exhibits a watery feature of a
different complexion: here the entire interior is charged with such a
supply of liquid, that, when cut, it affords a copious and refreshing
beverage to man. That these extraordinary sources of "living springs of
water" are not unknown to inferior creation, is a fact interestingly
confirmed to us in the happy incidents detailed by Mr. Campbell, in his
_Travels in South Africa_, where a species of mouse is described
to us, as storing up supplies of water contained in the berries of
particular plants; and, in Ceylon, animals of the _S_ímia tribe are
said to be well acquainted with the _N_epénthes distillatòria, and
to have frequent recourse to its pitcher. The mechanism of the "rose of
Jericho" (Anastática hierochuntìna] shows the susceptibility of plants
to moisture in a very remarkable manner; and I have submitted some
experiments made with this extraordinary exotic, the inhabitant of an
arid sandy soil, to the Horticultural Society of London. That succulents
should be found clothing in patches the surface of the burning desert is
a phenomenon not the least wonderful in the geographical history of
vegetation.
In Cockburn's _Voyages_ we find an interesting account of a tree in
South America, which yielded a plentiful supply of water by a kind of
distillatory process: this tree was met with near the mountainous
district of Vera Paz. The party were attracted to it from a distance,
the ground appearing wet around it; and the peculiarity was the more
striking, as no rain had fallen for six months previous. "At last," says
he, "to our great astonishment, as well as joy, we saw water dropping,
or, as it were, distilling fast from the end of every leaf of this
wonderful tree; at least it was so with us, who had been labouring four
days through extreme heat without receiving the least moisture, and
were now almost expiring for want of it." The testimony of travellers
is too often enshrined among the fabulous; and their credentials either
altogether rejected by some, or at least received "cum grano salis."
Bruce of Kinnaird forms the most remarkable example of this kind, and
the caricature of Baron Munchausen consigned the whole to sarcasm
and ridicule; and yet the time is come when the more remarkable
circumstances and phenomena mentioned by this traveller, verified by
Lord Valentia, Mr. Salt, &c. are received as well accredited facts.
The curious phenomenon mentioned by Cockburn finds an interesting and
beautiful counterpart in two plants--namely, the _C_álla Aethiópica
and Agapánthus umbellàtus, in both of which, after a copious watering,
the water will be seen to drop from the tips of the leaves; a
phenomenon, as far as I know, not hitherto recorded.
The great rivers of the continent of Europe have their source of supply
in the glaciers; but many of the rivers in the New World owe their
origin to the extensive forests of America, and their destruction might
dry up many a rivulet, and thus again convert the luxuriant valley into
an arid and sterile waste; carried farther, the principle extends to the
great features of the globe. What the glaciers effect among the higher
regions of the Alps, the _P_ìnus _Cémbra_. and _L_árix commùnis
accomplish at lower elevations; and many a mountain rivulet owes its
existence to their influence. It rains often in the woodlands when it
rains no where else; and it is thus that trees and woods modify the
hygrometric character of a country; and I doubt not but, by a judicious
disposal of trees of particular kinds, many lands now parched up with
drought--as, for example, in some of the Leeward Islands--might be
reclaimed from that sterility to which they are unhappily doomed.
In Glass' _History of the Canary Islands_ we have the description
of a peculiar tree in the Island of Hierro, which is the means of
supplying the inhabitants, man as well as inferior animals, with water;
an island which, but for this marvellous adjunct, would be uninhabitable
and abandoned. The tree is called _Til_ by the people of the island,
and has attached to it the epithet _garse_, or _sacred_. It is situated
on the top of a rock, terminating the district called _Tigulatre_,
which leads from the shore. A cloud of vapour, which seems to rise from
the sea, is impelled towards it; and being condensed by the foliage of
the tree, the rain falls into a large tank, from which it is measured
out by individuals set apart for that purpose by the authorities of
the island.
In confirmation of a circumstance _primâ facie_ so incredible,
I have here to record a phenomenon, witnessed by myself, equally
extraordinary. I had frequently observed, in avenues of trees, that the
entire ground engrossed by their shady foliage was completely saturated
with moisture; and that during the prevalence of a fog, when the ground
without their pale was completely parched, the wet which fell from their
branches more resembled a gentle shower than anything else; and in
investigating the phenomenon which I am disposed to consider entirely
_electrical_, I think the _elm_ exhibits this feature more
remarkably than any other tree of the forest. I never, however, was more
astonished than I was in the month of September last, on witnessing a
very striking example of this description. I had taken an early walk, on
the road leading from Stafford to Lichfield: a dense fog prevailed, but
the _road was dry and dusty_, while it was quite otherwise with
the line of a few _Lombardy poplars_; for from them it rained so
plentifully, and so fast, that any one of them might have been used as
an admirable shower bath, and the constant stream of water supplied by
the aggregate would (had it been directed into a proper channel) have
been found quite sufficient to turn an ordinary mill.--_Mag. Nat.
Hist._
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