J. C. (John Claudius) Loudon.

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Online LibraryJ. C. (John Claudius) LoudonAn encyclopaedia of gardening; comprising the theory and practice of horticulture, floriculture, arboriculture, and landscape-gardening, including all the latest improvements; a general history of gardening in all countries; and a statistical view of its present stat, with suggestions for its future → online text (page 48 of 313)
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produces one of the most magnificent of flowers j but blows only in the night ; and is hence known also
by the appellation of the night-blowing
cereus Some plants, such as the ferns,
algas, and fungi, are altogether destitute
of conspicuous flowers ; and are hence
called Cryptogamous ; but in this respect
the fig is perhaps the most singular. The
flowers which in other cases uniformly
precede the fruit, are in this case concealed
within what is generally denominated the
fruit ; as may be proved by cutting open a
green fig (fig.61. a) by means of a longitudi-
nal section passing through its axis. Great
numbers of flowers (6) are then disco-
vered lining a sort of cavity in the axis
of the fruit ; and hence what is called the
fruit or fig, in common language, is rather
the receptacle of the flower than any thing
else. Most plants have their flowers fur-
nished both with stamens and pistils, and
are hence hermaphrodites : but there are
also many genera that have the stamens
in one flower and the pistils in another,
both on the same individual ; these are
denominated Monoecious plants, and are
exemplified in the oak and hazel. Other
genera have the flowers with stamens on
one plant, and the flowers with pistils on
another ; these are denominated Dioeci-
ous, and are exemplified in the hop and willow. Others have flowers of all the previous kinds on one and
the same plant ; these are denominated Polygamous, and are exemplified in the genus Atriplex.

807. The fruit. The anomalies of the fruit may affect either its number, figure, color,
or appendages. The common hazel-nut produces in general but one kernel in one shell ;
but in the course of opening up a considerable number, you will now and then meet with
one containing two or three kernels in a shell.

This is perhaps best accounted for by supposing, with Du Hamel, that
it is the result of an unnatural graft effected in the bud ; though some
think that the shell does always contain the rudiments of two or more
kernels, although it rarely happens that more than one is developed.
But if two apples or pears are developed in an incorporated state, which
is a case that now and then occurs, it is no doubt best accounted for by
the graft of Du Hamel. Sometimes the anomaly consists in the figure
of the fruit, which is deformed by tumors or excrescences, in conse-
quence of the bite of insects, or injuries of weather producing warts,
moles, or specks. Sometimes it consists in the color, producing green
melons and white cucumbers. Sometimes it consists in an appendage of
leaves. (Jig. 62.)

808. Habit. Some plants, which, when placed in a rich
soil, grow to a great height and affect the habit of a tree,
are, when placed in a poor soil, converted into dwarfish
shrubs.

This may he exemplified in the case of the box-tree ; and so also in the case of herbaceous plants : as in
IK J?I 8 ' Wh, * h k 1 " l ry s il uatlon . s i s but short and dwarfish, while in moist situations it grows to
bv m a f of ,.H ?tt b * l ? lt0gether a dlffe ^ ent u Plant The habit of the P lant is sometimes totally altered
St^Sna thn. TV* he Py ru / co mun 1 ls i When growing in a wildand uncultivated state, is furnished
with strong thorns ; but when transferred to a rich and cultivated soil the thorns disaonear This
&?3SSSi2;?lS KfiSS & Unn A^> WaS regarded as being eStaientto[he tatmj oYanimat
in nlace ^Irtih %Jnt WMM herS w-* Sa , me g u Gat botanist > ch more plausible thin profound,
Med state of Kf or denow substitutes the following: The thorns protruded in the uncul!
with \b t sufficiencJ rftihif rendered abortive from want of nourishment, which when supplied
wiin a sumciency ot nourishment, are converted into leaves and branches.

809. Physical virtues. When plants are removed from their native soil and taken
into a state of culture, it alters not only their habit but their physical virtues. Thus the
sour grape is rendered sweet, the bitter pear pleasant, the dry apricot pulpy, the prickly





Book I.



SEXUALITY OF VEGETABLES.



181



lettuce smooth, and the acrid celery wholesome. Pot-herbs are also rendered more tender
by means of cultivation, and better fitted for the use of man ; and so also are all our fine
varieties of fruit.

810. Duration. Plants are either annuals, biennials, or perennials, and the species is
uniformly of the same class. But it has been found that some plants which are annuals
in a cold climate, such as that of Sweden, will become perennials in a hot climate, such
as that of the West Indies ; this anomaly has been exemplified in tropaeolum, beet-root,
and malva arborca : and, on the contrary, some plants, which are perennials in hot climates,
are reduced to annuals when transplanted into a cold climate ; this has been exemplified
in ricinus.

Sect. VI. Of the Sexuality of Vegetables.

811. The doctrine that plants are of different sexes, and winch constitutes the found-
ation of the Linnean system, though but lately established upon the basis of logical in-
duction, is by no means a novel doctrine. It appears to have been entertained even
among the original Greeks, from the antiquity of their mode of cultivating figs and palms.
Aristotle and Theophrastus maintain the doctrine of the sexuality of vegetables; and
Pliny; Dioscorides, and Galen, adopted the division by which plants were then distributed
into male and female ; but chiefly upon the erroneous principle of habit or aspect, and
without any reference to a distinction absolutely sexual. Pliny seems to admit the dis-
tinction of sex in all plants whatever, and quotes the case of the palm-tree as exhibiting
the most striking example.

812. Discoveries of the moderns. Ca?salpinus, in the sixteenth century, denominates trees which pro-
duce ffuit only, females ; and trees of the same kind which are barren, males ; adding, that the fruit is
found to be more abundant and of a better quality where the males grow in the neighbourhood of the
females, which is, he says, occasioned by certain exhalations from the males dispersing themselves -all
over the females, and by an operation not to be explained, disposing them to produce more perfect seed.
About the middle of the seventeenth century, the doctrine of the sexes of the plants began to assume a
more fixed and determinate character. Malpighi describes the stamens, anthers, and pollen : the merit of
suggesting the use of the latter seems to be between Sir T. Millington, Savilian Professor at Oxford, and
the celebrated Dr. Grew. The "opinion of Grew was adopted also by Ray. The first example of experi-
ment recorded on this subject is that of Camerarius, professor of botany at Tubingen, who having
adopted the opinions of Grew and Raj-, though without perhaps regarding their arguments as the best that
could be adduced, conceived that the subject might be still further illustrated by means of depriving the
plant of its male flowers altogether, or of removing the individuals of a different sex to a distance from
one another. Accordingly having selected some plants of mercurialis, morus, zea mays, and ricinus,
and stripped them of their staminiferous flowers, or removed the male plant to a great distance from the
female, he found that the fruit did not now ripen ; the inference from which was, that the generation of
plants is analogous to that of animals, and that the stamens of the flowers of the former correspond to the
sexual organs of the males of the latter. The great and illustrious Linnaeus, reviewing with his usual
sagacity the evidence on which the doctrine rested, and perceiving that it was supported by a multiplicity
of the most incontrovertible facts, resolved to devote his labors peculiarly to the investigation of the
subject, and to prosecute his enquiries throughout the whole extent of the vegetable kingdom ; which great
and arduous enterprise he not only undertook but accomplished with a success equal to the unexampled
industry with which he pursued it. So that by collecting into one body all the evidence of former dis-
covery or experiment, and by adding much that was original of his own, he found himself at length
authorised to draw the important conclusion that no seed is perfected without the previous agency of
the pollen ; that the doctrine of the sexes of plants is consequently founded in fact.

813. Proofs from the economy of the aquatics. Many
plants of this class that vegetate for the most part wholly
immersed in water, and often at a considerable depth,
gradually begin to elevate their stems as the season of*
flowering advances, when they at last rear their heads
above the surface of the water, and present their opening
blossoms to the sun, till the petals have begun to fade,
when they again gradually sink down to the bottom to
ripen and to sow their seeds. This very peculiar economy
may be exemplified in the case of ruppia maritima, and
several species of potamogeton, common in our ponds
and ditches ; from which we may fairly infer, that the
flowers rise thus to the surface merely to give the pollen
an opportunity of reaching the stigma uninjured. But
the most remarkable example of this kind is that of the
valisneria spiralis {fig. 63.), a plant that grows in the
ditches of Italy. The plant is of the class Dicecia, pro-
ducing its fertile flowers on the extremity of a long and
slender stalk twisted spirally like a corkscrew, which-
uncoiling of its own accord, "about the time of the open-
ing of the blossom, elevates the flowers to the surface of
the water, and leaves them to expand in the open air.
The barren flowers are produced in great numbers upon
short upright stalks issuing from a different root, from
which they detach themselves about the time of the
expansion of the female blossom, mounting up like little
air bubbles, and suddenly expanding when they reach the surface, where they float about in great
numbers among the female blossoms, and often cling to them in clusters so as to cover them entirely ;
thus bringing the stamens and pistils into immediate contact, and giving the anthers an opportunity of
discharging their pollen immediately over the stigma. When this operation has been performed, the now
uncoiled stalk of the female plant begins again to resume its original and spiral form, and gradually sinks
down, as it gradually rose, to ripen its fruit at the bottom of the water. We have gathered (in 1819)
these stalks, in the canals near Padua, upwards of ten feet long.




N 3



J82 SCIENCE OF GARDENING. Part II.

Sect. VII. Impregnation of the Seed. t

814. The stamens and pistils are the male and female organs of vegetable generation, and
tlie pollen is the substance by which the impregnation of the seed is effected ; but how is the
pollen conveyed to the ovary ? And what is the amount of its action ?

815. Access of the pollen. When the stamens and pistils are situated near each other, the elastic spring
with which the anther flies open will generally be sufficient to disperse the pollen, so as that part of it
must infallibly reach the stigma in such flowers as do not perfect their stamens and pistils at the same
time. The pollen is very generally conveyed from the anther to the stigma through the instrumentality of
bees, and other insects peculiar to a species. The object of the insect is the discovery of honey, in quest of
which, whilst it roves from flower to flower, and rummages the recesses of the corolla, it unintentionally
covers its body with pollen, which it conveys to the next flower it visits, and brushes off' as it acquired it by
rummaging for honey ; so that part of it is almost unavoidably deposited on the stigma, and impregnation
thus effected. Nor is this altogether so much a work of random as it at first appears. For it has been
observed that even insects, which do not upon the whole confine themselves to one species of flower, will
yet very often remain during the whole day upon the species they happen first to alight on in the morning ;
hence the impregnation of the females of Dioecious plants where no male is near. Hence also a sort of
natural crossing of the breed of plants which might probably otherwise degenerate.

816. Fecundation of the ovary. Admitting that the pollen is conducted to the ovary
through the channel of the tubes of the style, how after all is the ovary fecundated ; or
the seed rendered fertile ? On this subject naturalists have been much divided ; and ac-
cording to their several opinions have been classed under the respective appellations of
ovarists, animalculists, and epigenesists,

817. Ovarist. According to the opinion of the Ovarist, the embryo pre-exists in the ovary, and is
fecundated by the agency of the pollen as transmitted to it through the style.

818. Animalculist. But the theory of the ovarists is not without its difficulties ; for as the embryo is
never found to make its appearance till after fecundation, it has been thought that it must necessarily pre-
exist in the pollen of the anther; from which it is conveyed to the ovary through the medium of the style,
and afterwards matured. This theory was founded upon that of Leuwenhoeck, with regard to animal
generation ; which supposes the pre-existence of animalcula in the seminal principle of the male ; the
animalcula being conveyed in coitu to the ovary of the female, where alone they are capable of
developsment.

819. Epigenesist. The difficulties inseparable from both theories, together with the phenomenon of
hybrid productions, have given rise also to a third ; this is the Theory of the Epigenesists, who maintain that
the embryo pre-exists neither in the ovary nor pollen, but is generated by the union of the fecundating
principles of the male and female organs ; the former being the fluid issuing from the pollen when it
explodes; and the latter, the fluid that exudes from the surface of the stigma when mature. But if
the seed is generated from the union of two fecundating principles which form an intermediate offspring,
then female plants of the class Dicecia ought occasionally to produce seeds whose offspring shall be Her-
maphrodite, or at least Monoecious, which was never yet known to happen.

820. Hybrids. Although the arguments of the epigenesists are by no means satis-
factory, yet it cannot be denied, that hybrid productionstpartake of the properties both of
the male and female from which they spring. This was long ago proved to be the fact
by Bradley, and more recently confirmed by the experiments of Knight ; as well as hap-
pily converted to the advantage of the cultivator.

821. Vegetable crossing. Observing that farmers who rear cattle improve the progeny by means of crossing
the breed, Knight argued from analogy-, that the same improvement might be introduced into vegetables.
His principal object was that of procuring new and improved varieties of the apple and pear to supply the
place of such as had become diseased and unproductive. But as the necessary slowness of all experiments
of the kind, with regard to the fruit in question, did not keep pace with the ardor of his desire to obtain in-
formation on the subject, he was induced to institute some tentative experiments upon the common pea,
a plant well suited to his purpose, both from its quickness of growth, and from the many varieties in form,
size, and color, which it afforded. In 1787, a degenerate sort of pea was growing in his garden, which had
not recovered its former vigor even when removed to a better soil. Being thus a good subject of experiment,
the male organs of a dozen of its immature blossoms were destroyed, and the female organs left entire!
When the blossoms had attained their mature state, the pollen of a very large and luxuriant grey pea was
introduced into the one half of them, but not into the other. The pods of both grew equally ; but the seeds
of the half that were unimpregnated withered away, without having augmented beyond the size to which
they had attained before the blossoms expanded. The seeds of the other half were augmented and
matured as in the ordinary process of impregnation ; and exhibited no perceptible difference from those
of other plants of the same variety ; perhaps because the external covering of the seed was furnished
entirely by the female. But when they were made to vegetate in the succeeding spring, the effect of
the experiment was obvious. The plants rose with great luxuriance, indicating in their stem, leaves, and
fruit, the influence of this artificial impregnation ; the seeds produced were of a dark grey. By im-
pregnating the flowers of this variety with the pollen of others, the color was again changed, and new
varieties obtained, superior in every respect to the original on which the experiment was first made and
attaining in some cases, to a height of more than twelve feet. (Phil. Trans. 1789.) Knight thinks his
experiments on this subject afford examples of superfoetation, a phenomenon, the existenceof which has
been admitted amongst animals, but of which the proof amongst vegetables is not yet quite satisfactory
Of one species of superfoetation he has certainly produced examples ; that is, when, by impregnating a
white pea-blossom with the pollen both of a white and grey pea, white and grey seeds were obtained
But of the other species of superfoetation, in which one seed is supposed to be the joint issue of two males
the example is not quite satisfactory. Such a production is perhaps possible, and further experiments'
may probably ascertain the fact ; but it seems to be a matter of mere curiositv, and not apparently con
nected with any views of utility.

822. The practicability of improving the species, is rendered strikingly obvious bv these experiments -
and the ameliorating effect is the same whether by the male or female ; as was ascertained by impreg-
nating the largest and most luxuriant plants with the pollen of the most diminutive and dwarfish or
the contrary. By such means any number of varieties may be obtained, according to the will of the
experimenter, amongst which some will no doubt be suited to all soils and situations Knight's ex
penments of this kind were extended also to wheat; but not with equal success. For though some
very good varieties were obtained, yet they were found not to be permanent. But the success of his
experiments on the apple-tree were equal to his hopes. This was indeed his principal object and no
means of obtaining a successful issue were left untried. The plants which were obtained in this eafe



Book I. IMPREGNATION OF VEGETABLE& 183

were found to possess the good qualities of both of the varieties employed, uniting the greatest health
and luxuriance with the finest and best-flavoured fruit.

823. Improved varieties of every fruit and esculent plant may be obtained by means of artificial impreg-
nation, or crossing, as they were obtained in the cases already stated. Whence Knight thinks, that this
promiscuous impregnation of species has been intended by nature to take place, and that it does in fact
often take place, for the purpose of correcting such accidental varieties as arise from seed, and of con-
fining them within narrower limits. All which is thought to be countenanced from the consideration of
the variety of methods which nature employs to disperse the pollen, either by the elastic spring of the
anthers, the aid of the winds, or the instrumentality of insects. But, although he admits the existence
of vegetable hybrids, that is, of varieties obtained from the intermixture of different species of the same
genus, yet he does not admit the existence of vegetable mules, that is, of varieties obtained from the
intermixture of the species of different genera ; in attempting to obtain which he could never succeed,
in spite of all his efforts. Hence he suspects that where such varieties have been supposed to take place,
the former must have been mistaken for the latter. It may be said, indeed, that if the case exists in the
animal kingdom, why not in the vegetable kingdom ? to which it is, perhaps, difficult to give a satisfactory
reply. But from the narrow limits within which this intercourse is in all cases circumscribed, it scarcely
seems to have been the intention of nature that it should succeed even among animals. Salisbury is of a
different opinion, and considers [Hart. Trans, i. 364.) that new species may be created both by bees and
the agency of man ; and the recent experiments of Herbert, Sweet, and others seem to confirm this
opinion. Sweet's experience leads him to conclude that the plants of all orders strictly natural may be
reciprocally impregnated with success, and he has already, in the nursery-gardens of Messrs. Colvill,
produced many new gerania? and rhodracea?.

I singular or anomalous effect of crossing, or extraneous impregnation, is the change sometimes un .
dergone by the seed or fruit which is produced by the blossom impregnated. These effects are not uniform
results, but they are of frequent occurrence, and have attracted notice from a very early period. John Tur-
ner observes [Hort. Trans, v. 65.) that Theophrastus and Pliny {Theophrast. Hist. Plant. L ii. c.4. ; PliniiHist.
Nat. 1. xvii. c. 25.) seem to allude to it, and that the notion was entertained by Bradley, who, in his
New Improvements in Planting and Gardening, after giving directions for fertilising the female flowers
of the hazel with the pollen of the male, says, " By this knowledge we may alter the property and taste
of any fruit, by impregnating the one with the farina of another of the same class, as, for example, a
codlin with a pearmain, which will occasion the codlin so impregnated to last a longer time than usual,
and be of a sharper taste ; or if the winter fruit should be fecundated with the dust of the summer kinds,
they will decay before their usual time ; and it is from this accidental coupling of the farina of one kind with
the other, that in an orchard, where there is variety of apples, even the fruit gathered from the same tree
differs in its flavor and times of ripening; and, moreover, the seeds of those apples so generated, being
changed by that means from their natural qualities, will produce different kinds of fruit, if they are sown."
Turner, after quoting several' instances, and, among others, one from the Philosophical "Transactions
" concerning the effect which the farina of the blossoms of different sorts of apples had on the fruit of
a neighbouring tree," states upwards of six cases of hybridised apples, that had come within his own
observation, and concludes with the remark, that if there does exist in fruits such a liability to change,
it wdl at once be evident to the intelligent cultivator how much care is requisite in growing melons,
cucumbers, &c. to secure their true characters, even without reference to saving seed for a future crop.
In the same volume of the Horticultural Transactions [p. 234.), an account is given of different-colored
peas being produced in the same pod by crossing the parent blossom. All these facts seem to contradict
the generally received opinion, that crossing only affects the next generation ; here it appears to affect
the embryo offspring ; and a gardener who had no keeping apples in his orchard, might communicate
that quality in part to his summer fruit by borrowing the use of a neighbour's blossoms from a late variety.
It is probable, however, that such counter-impregnations do not take place readily ; otherwise the produce
of a common orchard would be an ever-varying round of monstrosities.

Sect. VIII. Oianges consequent upon Impregnation.
825. The peculiar changes consequent upon impregnation, whether in the flowers or
fruit, may be considered as external and infernal.

826. External changes. At the period of the impregnation of the ovary the flower has attained to Its
ultimate state of perfection, and displayed its utmost beauty of coloring and richness of perfume. But as
it is now no longer wanted, so it is no longer provided for in the economy of vegetation. Its period of
decline has commenced ; as is indicated, first by the decay of the stamens, then of the petals, and then of
the calyx, which wither and shrink up, and finally detach themselves from the fruit altogether, except in
some particular cases in which one or other of them becomes permanent and falls only with the fruit. The
stigma exhibits also similar symptoms of decay, and the style itself often perishes. 'The parts contiguous
to the flower, such as the bractes and floral leaves, are sometimes also affected ; and finally the whole
plant, at least in the case of annuals, begins to exhibit indications of decay. But while the flower withers
and falls, the ovarv is advancing to perfection, swelling and augmenting in size, and receiving now all the



Online LibraryJ. C. (John Claudius) LoudonAn encyclopaedia of gardening; comprising the theory and practice of horticulture, floriculture, arboriculture, and landscape-gardening, including all the latest improvements; a general history of gardening in all countries; and a statistical view of its present stat, with suggestions for its future → online text (page 48 of 313)