Plants, as well as animals, are organised bodies, and like them their
parts may be dissected and decomposed by art; but the anatomy of the
former has not been cultivated so long and with so much zeal and
success as that of animals. Some naturalists, about the beginning of
the last century, first began to make it an object of attention, to
compare the structure of plants with that of animals; and for that
purpose to employ the microscope. Among these, two distinguished
themselves in a particular manner; Marcellus Malpighi, an Italian;
and Nehemiah Grew, an Englishman; who both undertook almost the same
experiments and made them known at the same time; so that it is
impossible to determine which of them was the earlier. It appears,
however, that Grew published some of his observations a little sooner;
but Malpighi was prior in making his known in a complete manner. But
even allowing that the one had received hints of the processes of the
other, they are both entitled to praise that each made experiments of
his own, and from these prepared figures, which are always more correct
the nearer they correspond with each other.
Among the various helps towards acquiring a knowledge of the anatomy
of plants, one of the principal is the art of reducing to skeletons
leaves, fruit and roots; that is, of freeing them from their soft,
tender and pulpy substance, in such a manner, that one can survey alone
their internal, harder vessels in their entire connexion. This may be
done by exposing the leaves to decay for some time soaked in water, by
which means the softer parts will be dissolved, or at least separated
from the internal harder parts, so that one, by carefully wiping,
pressing and rinsing them, can obtain the latter alone perfectly
entire. One will possess then a tissue composed of innumerable woody
threads or filaments, which, in a multiplicity of ways, run through
and intersect each other. By sufficient practice and caution one may
detach, from each side of a leaf, a very thin covering, between which
lies a delicate web of exceedingly tender vessels. These form a woody
net-work, between the meshes of which fine glandules are distributed.
This net is double, or at least can be divided lengthwise into halves,
between which may be observed a substance that appears as it were to be
the marrow of the plant. Persons who are expert often succeed so far,
with many leaves, as to separate the external covering on both sides
from the woody net, and to split the latter into two, so that the whole
leaf seems to be divided into four.
One might conjecture that this method of reducing leaves to skeletons
must have been long known, as one frequently finds in ponds leaves
which have dropped from the neighbouring trees, and which by
decomposition, without the assistance of art, have been converted into
such a woody net-work, quite perfect and entire. It is however certain
that a naturalist, about the year 1645, first conceived the idea of
employing decomposition for the purpose of making leaf-skeletons, and
of assisting it by ingenious operations of art.
This naturalist, Marcus Aurelius Severinus, professor of anatomy and
surgery at Naples, was born in 1580, and died of the plague in 1656.
In his Zootomia Democritæa, printed in 1645, he gave the figure, with
a description of a leaf of the _Ficus Opuntia_ reduced to a skeleton.
Of the particular process employed to prepare this leaf, the figure
of which is very coarse and indistinct, he gives no account. He says
only that the soft substance was so dissolved that the vessels or
nerves alone remained; and that he had been equally successful with
a leaf of the palm-tree. A piece of a leaf of the like kind he sent
by Thomas Bartholin to Olaus Wormius, who caused it to be engraved on
copper, in a much neater manner, without saying anything of the method
in which it had been prepared[477]. The process Severin kept secret;
but he communicated it to Bartholin, in a letter, on the 25th of
February 1645, on condition that he would not disclose it to any one.
At that period, however, it excited very little attention, and was soon
forgotten, though in the year 1685 one Gabriel Clauder made known that
he had reduced vine-leaves, the calyx of the winter cherry, and a root
of hemlock, to a net or tissue by burying them in sand during the heat
of summer, and hanging them up some months in the open air till they
were completely dried.
This art was considered to be of much more importance when it was again
revived by the well-known Dutchman, Frederick Ruysch. That naturalist
found means to conduct all his undertakings and labours in such a
manner as to excite great wonder; but we must allow him the merit of
having brought the greater part of them to a degree of perfection
which no one had attained before. By the anatomy of animals, in which
he was eminently skilled, he was led to the dissection of plants; and
as it seemed impossible to fill their tender vessels, like those of
animals, with a coloured solid substance[478], he fell upon a method of
separating the hard parts from the soft, and of preserving them in that
manner.
For this purpose he first tried a method which he had employed with
uncommon success, in regard to the parts of animals. He covered the
leaves and fruit with insects, which ate up the soft or pulpy parts,
and left only those that were hard. But however well these insects,
which he called his little assistants, may have executed their task,
they did not abstain altogether from the solid parts, so that they
never produced a complete skeleton. He dismissed them, therefore, and
endeavoured to execute with his own fingers what he had before caused
the insects to perform, after he had separated the soft parts from the
hard by decomposition. In this he succeeded so perfectly, that all who
saw his skeletons of leaves or fruit were astonished at the fineness of
the work and wished to imitate them.
I cannot exactly determine the year in which Ruysch began to prepare
these skeletons. Trew thinks that it must have been when he was in a
very advanced age, or at any rate after the year 1718; for when he was
admitted to Ruysch’s collection in that year, he observed none of these
curiosities. Rundmann, however, saw some of them in his possession in
the year 1708[479]. At first Ruysch endeavoured to keep the process
a secret, and to evade giving direct answers to the questions of the
curious. We are informed by Rundmann, that he attempted to imitate his
art by burying leaves at the end of harvest in the earth, and leaving
them there till the spring, by which their soft parts became so tender
that he could strip them off with the greatest ease. He produced also
the same effect by boiling them.
The first account which Ruysch himself published of his process,
was, as far as I know, in the year 1723. After he had sufficiently
excited the general curiosity, he gave figures of some of his
vegetable skeletons, related the whole method of preparing them, and
acknowledged that he had accidentally met with an imperfect engraving
of a leaf-skeleton in the Museum of Wormius, which had at one time
occasioned much wonder[480]. It is not improbable that he knew how the
Italian, whom he does not mention, though he is mentioned by Wormius,
and though he must certainly have been acquainted with his Zootomia,
prepared his skeletons. I must however observe, that it is remarked by
those who knew Ruysch, that he had read few books, and was very little
versed in the literature of his profession.
In the year following, Ruysch described more articles of the like kind,
and gave figures of some pears prepared in this manner. In 1726, when
Vater, professor at Wittenberg, expressed great astonishment at the
fineness of his works, he replied, in a letter written in 1727, that he
had at first caused them to be executed by insects, but that he then
made them himself with his fingers[481]. He repeated the same thing
also in 1728, when he described and gave engravings of more of these
curious objects[482]. The progress of this invention is related in the
same manner by Schreiber, in his Life of Ruysch.
When the method of producing these skeletons became publicly known,
they were soon prepared by others; some of whom made observations,
which were contrary to those of Ruysch. Among these in particular
were J. Bapt. Du Hamel, who, so early as the year 1727, described and
illustrated with elegant engravings the interior construction of a
pear[483]; Trew[484], in whose possession Keysler saw such skeletons
in 1730; P. H. G. Mohring[485]; Seba[486]; Francis Nicholls[487],
an Englishman; Professor Hollmann[488] at Göttingen, Ludwig[489],
Walther[490], Gesner[491] and others. Nicholls seems to have been the
first who split the net of an apple- or a pear-tree leaf into two equal
parts, though Ruysch split a leaf of the opuntia into three, four, and
even five layers, as he himself says.
In the year 1748, Seligmann, an engraver, began to publish, in
folio plates, figures of several leaves which he had reduced to
skeletons[492]. As he thought it impossible to make drawings
sufficiently correct, he took impressions from the leaves or nets
themselves, with red ink, and in a manner which may be seen described
in various books on the arts. Of the greater part he gave two figures,
one of the upper and another of the under side. He promised also to
give figures of the objects as magnified by a solar microscope; and two
plates were to be delivered monthly. Seligmann however died soon after,
if I am not mistaken; and a lawsuit took place between his heirs, by
which the whole of the copies printed were arrested, and for this
reason the work was never completed, and is to be found only in a very
few libraries.
Cobres says that eight pages of text, with two black and twenty-nine
red copper-plates, were completed. The copy which is in the library of
our university has only eight pages of text, consisting partly of a
preface by C. Trew, and partly of an account of the author, printed in
Latin and German opposite to each other. Trew gives a history of the
physiology of plants and of leaf-skeletons; and Seligmann treats on
the methods of preparing the latter. The number of the plates however
is greater than that assigned by Cobres. The copy which is now before
me contains thirty-three plates, printed in red; and besides these,
two plates in black, with figures of the objects magnified. Of the
second plate in red, there is a duplicate with this title, “Leaves of
a bergamot pear-tree, the fruit of which is mild;” but the figures in
both are not the same; and it appears that the author considered one
of the plates as defective, and therefore gave another. The leaves
represented in the plates are those of the orange-tree, lemon-tree,
shaddock-tree, butcher’s-broom, walnut-tree, pear-tree, laurel,
lime-tree, ivy, medlar, chestnut-tree, maple-tree, holly, willow, white
hawthorn, &c.
I shall take this opportunity of inserting here the history of the art
of raising trees from leaves. The first who made this art known was
Agostino Mandirola, doctor of theology, an Italian minorite of the
Franciscan order. In a small work upon Gardening, which, as I think,
was printed for the first time at Vicenza, in duodecimo, in the year
1652, and which was reprinted afterwards in various places, he gave
an account of his having produced trees from the leaves of the cedar-
and lemon-tree[493]; but he does not relate this circumstance as if
he considered it to be a great discovery. On the contrary, he appears
rather to think it a matter of very little importance. His book was
soon translated into German; and his account copied by other writers,
such as Böckler[494] and Hohberg[495], who were at that time much read.
A gardener of Augsburg, as we are told by Agricola, was the first who
imitated this experiment, and proved the possibility of it to others.
He is said to have tried it with good success in the garden of count de
Wratislau, ambassador at Ratisbon from the elector of Bohemia.
But never was this experiment so often and so successfully repeated as
in the garden of baron de Munchhausen, at Swobber. A young tree was
obtained there from a leaf of the _Limon a Rivo_, which produced fruit
the second year. It was sent to M. Volkamer, at Nuremberg, who caused
a drawing to be made from it, which was afterwards engraved, in order
that it might be published in the third volume of his Hesperides; but
as the author died too early, it was not printed. The exact drawing, as
it was then executed at Nuremberg, and an account of the whole process
employed in the experiment at Swobber, have been published by the baron
de Munchhausen himself, from authentic papers in his grandfather’s own
writing[496].
No one, however, excited so much attention to this circumstance as the
well-known George Andrew Agricola, physician at Ratisbon, who, with
that confidence and prolixity which were peculiar to him, ventured
to assert that trees could be propagated in the speediest manner by
planting the leaves, after being steeped in a liquor which he had
invented; and for the truth of his assertion he referred to his own
experiments[497]. Among the naturalists of that period none took more
trouble to examine the possibility of this effect than Thummig[498],
who endeavoured to prove that not only leaves with eyes left to them,
could, in well-moistened earth, throw out roots which would produce
a stem, but that leaves also without eyes would grow up to be trees.
Baron Munchhausen, on the other hand, assures us, that according to the
many experiments made in his garden, one can only expect young plants
from the leaves of those trees which do not bring forth buds; that
experiments made with the leaves of the lemon-tree had alone succeeded,
but never those made with the leaves of the orange- or lime-tree; and
that Agricola and Thummig had erroneously imagined that the leaves
themselves shot up into trees, their middle fibre (_rachis_) becoming
the stem, and the collateral fibres the branches. But the leaf decays
as soon as it has resigned all its sap to the young tree, which is
springing up below it.
To conclude: It is probable that the well-known multiplication of the
Indian fig, or _Opuntia_, gave the first idea of this experiment; for
every joint of that plant, stuck into the earth, and properly nurtured,
throws out roots and grows. As these joints were commonly considered to
be leaves, people tried whether other leaves would not grow in the like
manner. Luckily, those of the lemon-tree were chosen for this purpose;
and what was expected took place. Thus from a false hypothesis have new
truths often been derived; and thus was Kepler, by a false and even
improbable opinion, led to an assertion, afterwards confirmed, that
the periodical revolutions of the planets were in proportion to their
distance from the sun. But the raising of trees from leaves was too
rashly declared to be a method that might be generally employed; for it
is certain that it now seldom succeeds.
[Beckmann certainly overrates the value of these plant-skeletons in
assisting the acquirement of a knowledge of the anatomy of plants. By
macerating plants in water, all but the woody fibres are decomposed
by the putrefactive fermentation which ensues. From an examination of
these, a knowledge of structure merely is attainable, which may be
now truly said to be thoroughly understood. It gives us no insight
into its functions. The modern microscope has revealed to us the
structure of all the components of vegetable tissues, and has most
materially assisted in developing the functions of several; many,
however, remain in the hands of the physiologist. Nevertheless, these
plant-skeletons exhibit the true course and arrangement of the woody
fibres, and form most beautiful objects. The leaves are not the only
parts which can be thus prepared; the petals of many plants are even
more delicate and beautiful in their ligneous structure, as evidenced
in the hydrangea and several others. Their preparation is exceedingly
simple, but tedious, and can only be well effected by maceration in
water, which frequently requires to be considerably prolonged. The
pulpy half-decomposed portions are gradually removed by a camel-hair
pencil, or other means, with great delicacy and care; they are finally
washed and bleached, if necessary, with chloride of lime or soda. By
washing in considerably diluted muriatic acid and water, all traces of
this reagent are removed; they are then dried, and will keep for an
indefinite period.]