root, next ascends in th e form of a little twig, at th e same time sending downwards in the centre o f the
radicle, th e earliest portion of wood that is deposited, and compelling the root to emit little ramifications ;
and simultaneously the process of lignification is going on in all the tissue, by th e deposit of a peculiar
secretion in layers within the cells and tubes. Previously to th e elongation o f the plumule its point has
acquired the rudimentary state of a loaf: this latter continues to develope as the plumule elongates,
until, when the first internode of th e latter ceases to lengthen, the leaf has actually arrived a t its complete
formation. When fully grown it repeats in a much more perfect manner th e functions previously
performed by the cotyledons : it aerates the sap that it receives, and returns th e superfluous portion
of it downwards through the bark to the root ; tubular tissue at th e same time appears between the
medullary sheath and th e bark, thus forming th e first ligneous stratum, a part of whicli is incorporated
with the bark, the remainder forming wood. During these operations, while th e plumule is ascending,
’ ’ " ■■■ th e cellular its leaf forming and acting, and th e woody matter created by it descending, t tissue of the
stem is forming, and expanding horizontally to make room for the new matter forced into i t ; so that
develop.e.m.e.n.t. .is. g oing on simA u-lt aneously botK- -i-n- a horizontal and perp.e.n.d.i.cu..lar direction. This process may not inaptly be compared to that ol weaving, the warp being the perpendicular, and th e weft the
horizontal, formation. In order to enable the leaf to perform its functions of aeration completely, it
is traversed by veins originating in the medullary sheath, and has delicate pores (stOTnates), which
communicate with a liighly complex pneumatic system extending to almost every part of the plant.
Simultaneously with the appearance of woody matter, the emission of young roots, and th e ir increase by
addition to the cellular substance of their points takes place. They thus are made to bear something
like a definite proportion to tlie leaves they have to support, and with which they must of necessity be
in direct communication.
“ T k e p lum u le h a v in g pro d u c ed Us f i r s t leaf, others successively appear in a spiral direction around the
axis a t its growing point, all constructed alike, connected with the stem or axis in th e same manner, and
performing precisely the same functions as have been ju st described. At last th e axis ceases to lengthen ;
th e old leaves gradually fall off; th e new leaves, instead of expanding after their formation, retain their
rudimentary condition, harden, and fold over one another, so as to be a protection to th e delicate point
o f growth ; or, in other words, become th e scales of a bud. We have now a shoot with a woody
axis, and a distinct pith and bark ; and of a more or less conical figure. At the axil of every leaf a new
growing point had been generated during th e growth of th e axis ; so th a t th e shoot, when deprived of its
leaves, is covered from end to end with little, symmetrically arranged, projecting bodies, which are
the buds. The cause of th e figure of the perfect shoot being conical is, that, as th e wood originates
in the base of th e leaves, th e lower end of th e shoot, which has the greatest number of strata, because
it has the greatest number of leaves above it, will be the tliickest ; and th e upper end, which has had the
fewest leaves to distend it by their deposit, will have the least diameter. Thus th a t part of the stem
which has two leaves above it will have wood formed by two successive deposits ; th a t which has nine
leaves above it will have wood formed by nine successive deposits ; and so on : while the growing point,
as it can have no deposit of matter from above, will have no wood, th e extremity being merely covered
by the rudiments of leaves hereafter to be developed. If a t this time a cross section be examined, it
will be found that th e interior is no longer imperfectly divided into two portions, namely, pith and skin,
as it was when first examined in th e same way, but that it has distinctly two internal, perfect, concentric
lines, th e outer indicating a separation of the bark from th e wood ; and th e inner, a separation o i th e
wood from th e pith : th e latter too, which in th e first observation was fleshy, and saturated with humidity,
is become distinctly cellular, and altogether or nearly dry.
V egetation re commences with the spring of the second year and th e re turn of warm weather. The
uppermost, and perhaps some other buds, which were formed the previous year, gradually unfold, and pump
up sap from th e stock remaining in store about them ; th e place of th e sap so removed is instantly supplied
by th a t which is n ex t it ; an impulse is thus given to the fluids from th e summit to th e roots ; fresh
extension and fresh fibrils are given to th e roots; new sap is absorbed from the earth, and sent upwards
through th e wood of last year ; and th e phenomenon called the flow of the sap is fully completed, to
continue with greater or less velocity till th e return of w inter. The growing point lengthens upwards,
forming leaves and buds in th e same way as the parent shoot : th e horizontal increase of the whole
of the cellular system of the stem takes place, and each bud sends down organisable matter within the
bark and above the wood of the shoot from which it sprang ; thus forming on th e one hand a new layer
of wood, and on th e other a fresh deposit of liber. In order to facilitate this last operation, th e old bark
and wood are separated in the spring by th e exudation from both of them of th e glutinous, slimy substance
called cambium ; which appears to be expressly intended, in th e first instance, to facilitate the
developement of th e subcortical tubular tissue; and, in th e second place, to assist in generating the
cellular tissue by which th e horizontal dilatation of the axis is caused, and which maintains a communication
between the bark and the centre of th e stem. This communication has, by the second year,
become sufficiently developed to be readily discovered, and is effected b y th e medullary rays. It will be
remembered th a t there was a time when that which is now bark constituted a homogeneous body with
th e pith ; and that it was after th e leaves began to come into action th a t th e separation which now
exists between the bark and the pith took place. At th e time when they were indissolubly united
they both consisted of cellular tissue, with a few spiral vessels upon th e line indicative of future separation.
When a deposit of wood was formed from above between them they were not wholly divided
th e one from the other, but the deposit was effected in such a way as to leave a communication by
means of ce.l.l.u...l.a..r.. ..t.i.s..s..u..e.. ..b...e..t.w...e..e..n th e bark ’’ a nd’ th■ e p i th ; formation, or medullary ray, is
a t all times coetaneous with th a t of th e wood, the communication so e
between the pith and bark
is quite as perfect a t th e end of any number of years as it was at th e beginning of the ii r s t ; and so it
■ ■’ ' ■’ ' • T h e sap which is drawn from the
continues to the end of the growth of th e plant. ^ B e_a_r_t_h_ _in_t_o c_i_r_c_u_l_a_ti_o_n
by the unfolding leaves is exposed, as m th e previous year, to the effect of air and lig h t; is then
returned through the petiole to the stem, and sent downwards through th e bark, to be from it either
conveyed to th e root, or distributed horizontally by the medullary rays to th e centre of th e stem. At
th e end of th e year the same phenomena occur as took place the first season: wood is gradually
deposited by slower degrees, whence the last portion is denser than the first, and gives rise to th e appearance
called th e annual zone s: th e new shoot or shoots are prepared for winter, and are again
elongated cones ; and the original stem has acquired an increase in diameter proportioned to the quantity
of - f new shoots which it produced, new shoots being to it now what young leaves were ' to ' “ it ’before. - -
“ The th ir d y e a r . All lII t
that took place the year before is repeated; more roots aj
„ . i r ; sap is 1 ^
absorbed by t"th e unfolding „ leaves;... , and ............its lo ' made ’ good ' ’
by new fluids introduced ...................... by ^ th e ____
roots
and transmitted through th e alburnum or wood of th e year before; new wood and liber are formed
from matter sent downwards by the buds ; cambium is ex u d e d ; the horizontal developement of cellular
tissue is repeated, but more extensively; wood towards th e end of th e year is formed more slowly, and
has a more compact character; and another ring appears indicative of this year’s increase. In p recisely
the same manner as in th e second and third years of its existence will the plant continue to
vegetate, till the period of its decay, each successive year being a repetition of the phenomena of that
which preceded it.
“ The age o f p u b e r ty . After a certain number of years th e tree arrives a t th e age of p u b e rty : the
period a t which this occurs is very uncertain, depending in some measure upon adventitious circumstances,
but more upon the idiosyncrasy, or peculiar constitution of the individual. About th e time
when this alteration of habit is induced, by the influence of which the sap or blood of th e plant is to be
partially diverted from its former courses into channels in which its force is to be applied to the production
of new individuals ra the r than to th e extension of itse lf;— about this time it will be remarked
th a t certain of th e young branches do not lengthen, as had been heretofore th e wont of others, but assume
a short stunted appearance, probably not growing two inches in the time which had been previously
sufficient to produce twenty inches of increase. Of these little stunted branches, called spurs, the te rminal
bud acquires a swollen appearance, and a t length, instead of giving birth to a new shoot, produces
from its bosom a cluster of twigs in the form of pedicels, each terminated by a bud, the leaves of which
are modified for th e purposes of reproduction, grow firmly to each other, assume peculiar forms and
colours, and form a flower, which had been enwrapped and protected from injury during the previous
winter by several layers of imperfect leaves, now brought forth as bracts. Sap is impelled into the
calyx through the peûicel by gentle degrees, is taken up by it, and exposed by the surface of its tube and
segments to air and light; but having very imperfect means of returning, all th a t cannot be consumed
by the calyx is forced onwards into th e circulation o fth e petals, stamens, and pistil. The petals unfold
themselves of a dazzling white tinged with pink, and expose the stamens; at the same time the disk
changes into a saccharine substance, which is supposed to nourish the stamens and pistil, and give them
energy to perform their functions.
“ P ro p a g a tio n . At a fitting time, th e stigmatic surface of the pistil being ready to receive the pollen,
th e latter Is cast upon it from th e anthers, which have remained near for that particular purpose. When
th e pollen touches the stigma, th e grains adhere by means of its viscid surface, emitting a delicate
membranous tiabe, which pierces into the stigmatic tissue, lengthens there, and conveys the matter con.
tained in the pollen towards the ovules, which th e tube finally enters by means of their foramina. This
has no sooner occurred than the petals and stamens fade and fail away, their ephemeral but important
functions being accomplished. The sap which is afterwards impelled through the peduncle can only be
disposed of to the calyx and ovary, where it lodges: both these swell and form a young fruit, which
continues to grow as long as any new matter of growth is supplied from the parent plant. At this time
th e surface of the fruit performs the functions of leaves in exposing the juice to light and air ; a t a subsequent
period, it ceases to decompose carbonic acid, gains oxygen, loses its green colour, assumes the
rich ruddy glow of maturity ; the peduncle, no longer a passage for fluids, dries up and becomes
unequal to supporting the fruit, which at last falls to the earth. Here, if not destroyed by animals, it
lies and decays : in the succeeding spring its seeds are stimulated into life, strike root in the mass of
decayed matter that surrounds tliem, and spring forth as new plants to undergo all the vicissitudes of
their parent.
“ Conclusion. Such are the progressive phenomena in the vegetation, not only of the apple, but of all
trees th a t are natives of northern climates, and of a large part of th e herbage of the same countries, —
modified, of course, by peculiarities of structure and constitution, as in annual and herbaceous plants,
and in those the leaves of which are opposite and not alternate ; but all the more essential circumstances
o f their growth are the same as those of the apple tree. If we reflect upon these phenomena, our minds
can scarcely fail to be deeply impressed with admiration a t the perfect simplicity, and, at tlie same time,
faultless skill with which all the machinery is contrived upon which vegetable life depends. A few
forms of tissue, interwoven horizontally and perpendicularly, constitute a stem ; the developement, by
th e first shoot that the seed produces, of buds which grow upon the same plan as the first shoot itself,
and a constant repetition of th e same formation causes an increase in the length and breadth of the
plant ; an expansion of the bark into a leaf, within wliich ramify veins proceeding from the seat of nutri.
tive matter in the new shoot, with a provision of air-passages in its substance, and of pores on its surface,
enables th e crude fluid sent from the roots to be elaborated and digested until it becomes the peculiar
secretion of the species ; the contraction of a branch and its leaves forms a flower ; the disintegration of
the internal tissue of a petal forms pollen ; th e folding inwards of a leaf is sufficient to constitute a
pistil ; and, finally, the gorging of the pistil with fluid which it cannot part with causes the production
of a fruit.
“ En d o g en o u s, o r monocotyledonous p la n ts . In hot latitudes there exists another race of trees, of which
palms are the representatives ; and in the north there are many herbs, in which growth, by addition to
th e outside, is wholly departed from, the reverse taking place ; th at is to say, their diameter increasing
by addition to the inside. As the seeds of such plants are formed with only ono cotyledon, they are
called monocotyledonous; and their growth being from the inside, they are also named endogenous.
In these plants th e functions of the leaves, flowers, and fruit are in nowise different from those of
th e apple; th e ir peculiarity consisting only in the mode of forming their stems. When a monocotyledonous
seed has vegetated, it usually does not disentangle its cotyledon from th e testa, but simply
protrudes th e collum and the radicle ; the cotyledon swelling, and remaining firmly encased in the
seminal integuments. The radicle shoots downwards to become root ; and a leaf is emitted from the
side of th e collum. This first lea4f4 i. s sJu cc4e eded b y anot her fac ing it,. a. nd. .a. r isintga from its a x il;, the second produces a third half facing it, and arising also from its a x i l ; and, in this manner, the spiral' production
of leaves continues, until the plant, if caulescent, is ready to produce its stem. Up to this
period no stem havi_nng _b__e_e_n fo„r—mI_e_d4.1,_ _it_ _h_a_s_ _n ecess arily -h . appened1 t•h at the bases of the leaves hitherto produced have been all upon nearly the same p lan e ; and as each has been produced from the bosom
of the other without any such intervening space as occurs in dicotyledonous plants, it would be impossible
for the matter of wood, if any were formed, to be sent downwards around the circumference
of the p la n t; it would, on the contrary, have been necessarily deposited in the centre. In point of
fact, however, no deposit of wood like t&at of dicotyledons takes place, either now or hereafter. The
union of the bases of the leaves has formed a flesliy stock, cormus, or plate , which, if examined, will
be found to consist of a mass of cellular tissue, traversed by perpendicular and horizontal bundles of
vascular and woody tissue, connected with the veins of th e leaves, of which they are manifest prolongations
downwards; and there is no trace of separable bark, medullary rays, or central p i th : th e whole
body being a mass of pith, woody, and vascular tissue, mixed together. To understand this formation vet
more clearly, consider for a moment the internal'structure of the petiole of a dicotyledon : it is composed
of a bundle or bundles of vascular tissue encased in pleurenchym, surrounded on all sides with pith or
which IS the same thing, parenchym. Now suppose a number of these petioles to be separated fr ’
their blades, and to be tied in a bunch parallel with each other, and. bv lateral nresRure. t.n he «nnee
so closely
bunch; if a transverse section ol tnese be made, it will exhibit the same mixture of bundles of woodv
tissue and parenchym, and the same absence of distinction between pith, wood, and bark, which has
been noticed m th e corm, or first plate, of monocotyledons.
ilades,and,by pressure,to be squeezed
sely together that their surfaces touch each other accurately, except a t the circumference of the
;of these loticed “ F o rm a tio n o fth e stems o f endogenous p la n ts . As soon as the plate has arrived at the necessary diameter,
it begins to lengthen upwards, leaving at its base those leaves that were before a t its circumference and
carrying upwards with it such as occupied its centre ; a t the same time, new leaves continue to be
generated at the centre, or, as it must now be called, a t the apex of the shoot. As fresh leaves are
developed, they th ru st aside to th e circumference those which preceded them, and a stem is bv degrees
produced. Since it has not been formed by additions made to its circumference by each successive leaf.
It IS not conical, as in dicotyledons; but, on th e contrary, as its increase has been a t the centre which
has no power to extend its limits, being confined by the circumference which, when once formed
does not afterwards materially alter in dimensions, it is, of necessity, cylindrical : and this is one of thè
marks by which a monocotyledon is often to be known in the absence of other evidence. The centre
being but little acted upon by lateral pressure, remains loose in texture, and, until it becomes verv old
does not vary much from the density acquired by it shortly after its formation; but the tissue of thè
circumference being continually jammed together by the pressure outwards of the new matter formed