having a fibre or fibres spirally generated in their inside.” (Ib id . p. 7.) Spiral vessels conveying air, and
ducts conveying sap, are the ordinary forms of this tissue.
L a tic ife ro u s tissue , o r c inenchym, “ consists of uninterrupted anastomosing tubes, having thick un marked
sides.” These vessels are largest in plants having milky juice, and smallest in those whose
juice is transparent. (See L in d l. In tr o d , to B o ta n y , 4th edit. (1848), vol. i. p. 91.)
Sect. II. Compound Organs o f Plants.
1043. The combination o f the elementary organs into masses, forms the compound or
external organs of plants.
1044. The compound organs o f flowering plants are easily recognisable, being the
roots, stems, branches, leaves, and other larger parts of plants; and also the cuticle,
liairs, scales, glands, piickles, and other smaller paits, which are found on the
larger. All the different paits of the flower and fmit are of course included in the
compound organs; and, in short, eveiy combination of vegetable tissue, which assumes
an uniform appearance in a jilant, and is, at the same time, a distinct p ait of it as a form,
aud not as a mere mass of tissue.
T he a x is o f a p la n t is a term that ought to be understood by the young gardener. In a seedling just
begun to grow, an elongation takes place at both ex tremities: the root, which strikes downwards in the
direction of the earth’s centre, is called the descending a x is ; and the stem, which shoots upwards in a
contrary direction, is the ascending axis. The point between the two is called the crown or collar.
Besides the stem and root, plants have a third movement, which acts horizontally and forms the medullary
system. Thus, “ when th e vital action of either spore, embryo, or bud is excited, th e tissue deve-
lopes in three directions : upwards, downwards, and horizontally.” (E lem . o f B o t. p. 24.)
The ro o t is useful not only to fix the plant in the earth, but to act as a reservoir of starchy and
glutinous matter for the support of the plant, and to absorb additional nourishment for it from the earth,
by means of its spongioles. Roots are always extensions of the woody tissue, and they have noleaf-buds.
A le a f bud, says Dr. Lindley, “ is a young plant produced without the agency of sexes, inclosed within
rudimentary leaves called scales, and developed on the outside of a stem.” ([IIbbiiCd .)'
T k e stem is produced by the successive development of leaf-buds, whieh cause a corresi
horizontal growth between them.” (/&7>. p .2 8 .) Stems are of four kinds : — Exogenous, which in?
crease by successive layers on the outside of the wood; Endogenous, which become more solid from
additions in the centre ; Acrogenous, which are formed by th e union of the bases of leaves, and the
extension of the point of the axis ; and Thallogenous, where no leaves or buds exist, and the stem
increases by simple elongation or dilation. “ In what are called Dictyogens, the stem has the structure
o f Endogens, and the root nearly that of Exogens.” (Ib id .)
Nodes are the places in a stem where leaves are developed, and buds are formed ; and inter-nodes are
th e sp.'ices between the nodes. Regular buds are found only in the axils of the leaves ; but sometimes
leaf-buds “ are found among the tissue of plants subsequently to the developement o fth e stem and leaves
and, without reference to the latter, are called latent, adventitious, or abnormal.” ( Ib id . p. 41.)
“ The m a n n e r in ivhich the leaves a r e fo ld ed in th e lea f-b u d varies in different species, and is called the
vernation o fth e plant.” (Ih id . p .42.)
Lea v e s a r e o fth e g r eate st im p ortanc e to plants, as it is in them th at most of the chemical changes in
th e fluids take place ; and hence, as D r. Lmdley observes, it is absolutely necessary to expose “ them to
th e full influence of light and air, for the purpose of securing a due execution of their natural functions.
Hence, also, the impropriety of mutilating plants by the destruction of their leaves. It is not, however,
to be understood that assimilation is dependent upon the mere number of leaves. iMany small ill-formed
leaves may be of less value to a plant than a few large healthy leaves. Secreting power is in proportion
to the ar ea of foliage, its health,x.sxA its proper exposure to lig h t a n d a ir , especially to air in motion ”
(Ib id . p. 57.)
1045. The leaves o f flowerless plants, such as ferns, are generally called fronds ; and
the wood of such as have arborescent trunks, such as the tree ferns, is o fth e kind called
Acrogenous, and is formed by the cohesion of the bases of the footstalks of the leaves, or
fronds, round a cellular axis. In the stmcture of mosses, neither vessels nor woody fibre
are employed ; their stems are of the kind called Thallogens, and consist entirely of
elongated ccUular tissue. 4.'lgæ and Fungi form the lowest orders of flowerless plants,
and theii* stmctiu’c consists almost entfrely of cellular tissue.
Chap. VI.
Vegetable Physiology, or the Action o f Plants.
1046. The laws o f vegetable life ought to be familiar to every gardener. He will find
these laws beautifully developed in various botanical works ; from which we shall here
give an abridgment of such paits as are calculated to be most useful to the cultivator,
and such as wo hope will induce him to pursue the subject farther by himself. We
shall first give a summaiy of the principal phenomena of vegetation; aud next, some
rcmai-lis relative to the actions of the different parts of plants.
Sect. I. The principal Phenomena o f Vegetation as exemplified in a single Plant.
1047. A seed in its dormant fiate, Dr. Lindley observes, “ may be regarded as a highly
carbonised body, possessing vitality, and capable of growing into a plant.” (Elements
o f Botany, 5th edit. p. 114.) I f the seed be properly ripe when gathered, and be kept
perfectly dry, its vitality may be suspended, without being destroyed, for an indefinite
length of time ; but “ if its chemical elements are unstably combined, thcir vitality is
quickly lost.” (Ibid.)
1048. Seeds in ripening become gradually hard and d iy ; and the preservation of
thcir vitality for a length of time depends upon the perfection of their maturation. As,
however, the first act of gennination is to reverse the process of maturation, seeds sown
before they are quite ripe germinate more quickly than those which ai’c fully ripe ; and
those which ai*e quite ripe germinate soonest if sown as soon as they ai*e gathered.
1049. Moisture, warmth, and air are essential to the germination o f a seed; and no seeds
will grow if any one of these tlu-ee conditions be wanting. Moisture and warmth without
afr will rot the seeds ; and wai-mth aud air without water wiU parch them ; but
they will not in either case produce plauts.
1050. The food o f plants consists of carbon in the form of carbonic acid ; nitrogen,
generally as ammonia ; and oxygen and hydrogen ; with a smaU quantity of earthy or
mineral matter, the natm-o of which varies according to the kind of plant.
1051. In the act o f germination the skin or outer covering of the seed, having been
softened by water, cracks; and tliis allows the embryo, which has had its vital force excited
by warmth, to swell, or, in other words, to expand and separate the particles of
concentrated carbon of which it principally consists. The carbon thus expanded has a
great affinity for oxygen, which it abstracts, partly from the water which it decomposes,
and partly from the air, the hydrogen aud nitrogen thus set free also appearing to
combine with the carbon of the seed. A sweet mucilage is now formed, in which are
found numerous vesicles or incipient cells, which are the nidiments of vegetable tissue.
1052. When a seed has germinated, the root appears fii'st, probably as it is tlu-ough the
root only that the plant can obtain food from the soil. The pai-t between the collar and
the cotyledons, which is called the caulicle, then begins to lengthen, straightening itself,
if it chances to be bent by the seed being badly placed, and generally raising the
cotyledons out of the earth, frequently with the integument or outer covering of the
seed still attached to them, especially iu the commoner species of the pine and fir tribe.
IVlien the cotyledons arc raised above the surface they soon expand, and, becoming
green, act as leaves. Sometimes, however, the cotyledons never escape from the integument
of the seed, but remain buried with it in the ground; and in tliis case the base ofthe
cotyledons lengthens, so as to allow the plumule to escape from between them, as in the
Araucaria imbricàta. (See Elements o f Botany, p. 116.)
1053. The temperature required to germinate seeds vai-ies from 32° to 80° or 90° ; and
some seeds, as those of the Aiistrahan acacias, may be immersed in water at the boiling
point without destroying vitality. The seeds of no plant will vegetate under 32°,
because below that degree water ft-eczes, and consequently could not be absorbed by the
tissue of the seed. The common annual grass (Pòa annua) will vegetate at, or very
slightly above, that temperature, as will the chickweed (Alsine mèdia), the common day
nettle (Làmium rùbrum), and various others. The seeds of wheat, bai-ley, rye, and beans,
have preseiwed their vitality at a temperature low enough to freeze mercury.
1054. The process o f malting barley is exactly the same as that of geiminating a seed.
By moistening the barley it swells, the starch of the cotyledon is changed into sugar, and,
being absorbed by the embiyo, the radicle is protmded at one end of the grain or seed,
and the plumule or commencement of the stem appears at the other. Here the process
is stopped, as the object is to retain in the malt the sweet mucilage foi-med by tlie act
of germination, and which would be dissipated by other chemical changes if the process
of vegetation were allowed to proceed.
1055. The circle o f vegetable life commences with the germination of a seed in the
soil, and ends with the decay of the plant which is produced by that seed. The foUowing
con-ect and beautiful pictm-e of the progress of a plant from infancy to matui-ity, is
given in Dr. Lindley’s own words, aud with his permission.
“ I f w e p la c e a seed,—that of an apple, for instance,—in earth a t the temperature of 32° Fahr., it will
remain inactive till it finally decays. But if it is placed in moist earth some degrees above 32° and
screened from th e action of light, its integument gradually imbibes moisture and swells, the tissue is
softened and acquires the capability of stretching, the water is decomposed, ancl a part of its oxygen
combining with the carbon of the seed, forms carbonic acid, which is expelled ; nutritious food for the
young parts is prepared by the conversion of starch into sugar, and th e vital action of the embryo
commences. It lengthens downwards by th e radicle, and upwards by the cotyledons ; the former
penetrating th e soil, the latter elevating themselves above it, acquiring a green colour by the defc’oormn
nproiasiiUtion nn noff tfhh«e, cf'aQrrblmonniifc' aancli/dl they a■bilisconir-bh tfernomm it-hKeo earth and atmosphere, a nd uni f_ol_d_i_n__gn i.n _ the
form of two opposite roundish leaves. This is the first stage of vegetation : the young plant consists
of little more than cellular tissue : only an imperfect developement of vascular and fibrous tissue
bemg discoverable, in th e form of a sort of cylinder lying just in the centre. The part within the
cylinder, a t its upper end, is now th e pith, without it th e bark ; while th e cylinder itself is th e preparation
for th e medullary sheath, and consists of vertical tubes passing through, and separated bv, cellular
tissue.
“ T h e y o u n g ro o t is now lengthening at its point, and absorbing from the earth its nutriment, which
passes up to th e summit of th e plant by the cellular substance, and is in part impelled into the cotyledons,
where it is aerated and evaporated, but chiefly urged upwards against the growing point or
plumule.
“ The p lum u le , forced onwards by the current of sap, which is continually impelled upwards from the
\ i : n
fl