1104. Parasitical mosses, liclmis, and fungi, may be placed in the first subdivision.
They are found as often, and in as great perfection on the stumps of rotten trees, and on
rotten pales and stakes, as on trees that ai*e yet vegetating ; whence it is also plain that
they do not derive thcir nom’ishmcnt from the juices of the plants on which they grow,
but from their decayed parts, and the atmosphere by which they ai-e sm-romided ; tho
plant to which they cling serving as a basis of support.
1105. Plants strictly parasitical may be placed in the second subdivision. By these
ai'c meant all such as do actually abstract from the juices of the plant to which they
cling, the nourishment necessaiy to the developement of their p a rts ; and of which the
most common, at least as being indigenous to Britain, are the mistletoe, dodder,
broom-rape, and a sort of tuber that grows on tbe root of saffron, and destroys it if
allowed to spread.
The Mistletoe ( Kiscutn álbum) is found for the most part on the apple-tree, the lime, the hawthorn, the
poplar, and some other trees. If its berry is made to adhere to the trunk, or branch of either of the
foregoing trees, which from its glutinous nature it may readily be made to do, it germinates by sending
out a small globular body attached to a pedicle, which after it acquires a certain length bends towards
the bark, into which it insinuates itself by means of a number of small fibres which it now protrudes,
...................................................................rt th e B • ■ . . . . . . . . .
nourishment necessary to its future developement. When
and by which it abstracts from the plant
the root has thus fixed itself in the bark tr
a t first smooth and tapering, and of a pale green colour, but
of the suDDorting supporting tree,, the _______ stem of the ..... , parasite .................. begins „
to ascend,
. it finally protruding 4------------------------ a m ultiplicity of branches
1
and leaves. It seems*to have been tfiought by some botanists that the ro o ts ^ f the mistletoe penetrate
even into the wood, as well as through the bark. But th e observations of Du Hamel show that this
opinion is not well founded. The roots are indeed often found within the wood, which they thus seem
to have penetrated by their own vegetating power. But
th e fact is, that they are merely covered by the additional
layers of wood that have been formed since the fibres
first insinuated themselves into the bark.
The Cùscuta europce'a, or Dodder (/?g. 244.), though
it is to be accounted a truly parasitical plant in the
issue, is yet not originally so. F or th e seed of this
p lant when it has fallen to th e ground takes root originally
by sending down its radicle into the soil and
elevating its stem into the air. It is not yet, therefore,
a parasitical plant. But the stem which is now elevated
above th e surface lays hold of the first plant it meets
with, though it is particularly partial to hops and nettles,
and twines itself around it, attaching itself by means
of little parasitical roots a t the points of contact, and
finally detaching itself from th e soil altogether by the
decay of th e original root, and becoming a truly parasitical
plant. Withering describes the plant in his arrangement
as being originally parasitical ; but this is certainly
not the fact.
T k e Orobdnche, or Broom-rape, which attaches itself
by the root to the roots of other plants, is also to be re garded
as being truly parasitical, though it sometimes
sends out fibres which seem to draw nourishment from
the ea rth. It is found most frequently on the roots of
the common broom.
1106. The structure and physiology o f true parasites will be found lucidly explained
by Dr. Broivn, in bis elaborate paper in tbe Linn. Trans., vol. xui. p. 227., on tbat
most wonderiltl of plants tbe Raffles/a Arnold/ ; and by J . E. Bowman, Esq., in an
equally elaborate paper (Linn. Trans., vol. xvi. p. 399—420) on the Latbi'Oì'a cquamària.
The majority of the tropical Orcbideae are true epiphytes.
1107. Plants partially parasitical have been lately discovered to exist among the
commonest British weeds. Tbese are of the nature of root parasites, and though they
have been long classed as noxious weeds, their real nature has been only recently
discovered. Among these parasites may be mentioned the eye-bright (Euphrasia), the
yellow rattle (Rhindntkus Cm ia galli), the cow-wheat (Melampyrum arvénse), and
Bdrtsia viscosa. AU these plants are singularly impatient of cultivation, though extremely
common on neglected grass lands.
1108. Light is a body which has veiy considerable influence on the structure of vegetables,
and some also on their habitation. The F u n g i do not require the usual interludes
of day, in order to decompose carbonic acid gas, and can live and thrive with little or no
light. In green plants, which require the action of light, the intensity reqnh'cd is veiy
different in different species : some require shady places, and hence the vegetable inhabitants
of caves, and the plants wliich grow in the shade of forests ; others, and the
greater number, require the direct action of the sun, and grow in exposed elevated sites.
De CandoUe considers that the great difficulty of cultivating Alpine plants in the gardens
of plains, arises from the impossibility of giving them at once the fresh temperatine and
intense light which they find on high mountains.
S e c t . I l l Civil Causes affecting the Distribution o f Plants.
1109. B y the art o f man, plants may be inured to circumstances foreign to their usual
habits. Tliough plants in general are limited to certain habitations destined for them by
nature, yet some ai-e, and probably the greater number may be, inm-ed to climates, soils,
aud situations, to which they are not indigenous. The means used are acclimatising
and culture.
1110. Acclimatising seems to be most easily effected, in going from a hot to a cold
climate, on herbaceous plants ; because it often happens that the frosts of winter are
accompanied by snow, which shelters the plant from the inclemency of the atmosphere
till the return of spring. Trees and shrabs, on the contrary, are acclimatised with
more difficulty, because they cannot be so easily sheltered from the cold, owing to the
greater length of their stems and branches. The acclimatising or naturalisation of
vegetables is to be attempted by two modes : by sowing the seeds of successive generations,
and by the difference of temperature produced by ditferent aspects. Experience,
however, has proved, that very little change takes place in the constitutions of plants, by
cither of these modes of treatment. An individual plant may be rendered more hardy,
or more delicate, by local or other changes ; but the power of the species to resist cold
or heat, di'ought or moisture, remains the same. Thus, the kidneybean, the nastui-tium,
the potato, and other plants from the southern hemisphere, though raised through
numerous generations by seed in Britain, ai*e as easily affected by the autumnal frosts as
they probably were when first planted in our gardens.
1111. Domesticated plants. “ Some plants,” Humboldt obseiwes, “ which constitute
the objects of gardening and of agriculture, have time out of mind accompanied man
from one end of the globe to the other. In Europe, the vine followed the Greelcs ; tho
wheat, the Romans ; and the cotton, the Ai-abs. In America, the Tultiques cairied
with them the maize ; the potato and the quinoa (Chenopodium Quinha, of which the
seeds are used,) are found wherever have emigrated the ancient Condinamarea. The
migration of these plants is evident ; but their first country is as little known as that of
the different races of men, which have been found in all parts of the globe fr'om the
earliest traditions. (Géogrophie des Plantes, p. 25.)
1112. The general effect o f culture on plants is that of enlarging all their parts ; but it
often also alters their qualities, fonns, and colours : it never, however, alters their primitive
structure. “ The potato,” as Humboldt observes, “ cultivated in Cliili, at nearly
twelve thousand feet above the level of the sea, carries the same flower as in Siberia.”
1113. The culinary vegetables o f our gardens, compared with the same species in their
wild state, afford striking proofs of the influence of culture on both the magnitude and
qualities of plants. Notliing, in regard to magnitude, is more remarkable than in the
case of the Frassica tribe ; and nothing, in respect to quality, exceeds the change
effected on the celery and caiTot.
1114. The influence o f culture on fru its is not less remarkable. The peach in its
wild state, in Medina, is poisonous ; but, cultivated in tbe plains of Ispahan and Egypt,
it becomes one of the most delicious of fruits. The effect of culture on the apple, peai-,
cherry, plum, and other fruits, is nearly as remarkable; for not only the frait and leaves,
but the general habits of the tree, arc altered in these and other species. The histoi-y of
the migration of fi-uit-trees has been commenced by Sickler, in a work ( Geschichte, &c.)
which Humboldt has praised as equally curious and philosophical.
1115. The influence o f culture on plants o f ornament is great in most species. The
parts of all plants are enlarged ; some arc nnmerically increased, as in the case of double
flowers : and, what is most remarkable, ei'cn the coloms are fi-equcntly changed, not
only in the flowers, bnt in the leaves and frait.
1116. The influence o f civilisation and culture, in increasing the number o f plants in a
country, is very considerable, and operates dfrectly, by introducing new species for culture
in gardens, fields or timber-plantations ; and, indirectly, by the acclimatising and
final naturalisation of many species, by the influence of winds and bfrds in scattering
thefr seeds. Tlie vine and the fig are not indigenous to France, but were brought
there by birds. In like manner the orange was naturalised in the south of Italy, and
many herbaceous plants of the Levant, both in Fi-ance and Britain ; some, as the
cabbage, cherry, and apple, probably during the subjection of England to tbe Romans.
The naiTow-leaved elm was brought from the Holy Land during the crusades. P h a sòolus
vulgaris and Falsamina hortcnsis were originaUy fr-om India ; and Datura
Stramonium, which is now naturalised in Eni-opc, came originaUy from India or
Abyssinia, Buckwheat, and most species of corn and peas, came also fr-om the East ;
and along with them several plants found among corn only, such as Centaui-ea Cyanus,
Agrostémma Githàgo, iiàphanus Raphanisti-um, and Afyagram sativum. The country
whence the most valuable gvasses migrated is not known. Bruce says he found the oat
wild in Abyssinia ; and wheat and millet have been found in a wild state in hiUy
situations in the East Indies. The Romans were unacquainted with either potatoes or
i-ye; and the native country of the fomier, Humboldt declares to be totally unknovm.
1117. The greatest refinement in culture consists in the successful formation o f artificial
climates for the culture of tropical plants in cold regions. Many vegetables, natives of
the toi-rid zone, such as the pine-apple, the palm, &c., cannot be acclimatised in tern-
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