Anatomy of the stem. A branch of this species, after attaining the age of two years and upwards, consists
principally of a soft white cellulai* tissue, occupying the axis of the plant and communicating with the thick bark by
means of broad medullary rays. The latter arc separated by woody plates, disposed in two concentric series, and
formed almost entii*ely of scalariform tissue with sometimes pleurenchyma. Cuticle. This is very stout in texture :
in a fii-st developed branch it consists of only one row of small cells (P late CVII. bis, / . I I ) these must be rapidly
added to, for after another year the cuticle of the same branch is of much gi*eater density and farmed of many series
of cells, much blended together, though] not so completely as to assume the appearance of a homogeneous tissue
without auy trace of cellulai'ity, which it afterwards attains (P late C V I I .//. 4, 5, aud 6). The cuticle is devoid
of stomata commonly so called, but furnished vrith numerous longitudinal prominences, each marked by a fissure.
A transverse section of one of these is given at P late CVII. / . 4, where the appearance is as of several layers of
cuticle superimposed and forming the prominence, becoming cellular towai-ds the centre, and depressed, pusliing
the subjacent epiphloeum before it. There is no actual stoma or communication between the external atmosphere
and tissue of the bark, fm-ther than what may be supposed to be afforded by cellular tissue, wliich is a
rapid conductor of moisture. These are verj» evident in the branches of the second year, no doubt answer to
stomata, whether performing the same functions or no, and are an instance either of the cuticle retaining its
originaUy cellular organization at the point where they occur, or revei-ting to that structure.
Bark. Tliis is composed almost entirely of a mass of cellular tissue, shrinking much when the stem is dry.
The epiphloeum is formed of several rows of transversely elongated thick-waUed cells, it occasionally contains air-
carities, but these are not so numerous or conspicuous as in M. punetulatum. The vessels of the liber are disposed
about half way between the cuticle and wood, are often very inconspicuous and fonned of scattered bundles of fibres
(P late CVII. / . 5 and 6 c.) protected by very thick-walled cells, as in most, if not all, the Loranthaceoe, at other
times they are in two series or variously disposed. This tissue does not appear to pass from one intei-node to
another, but to be interrupted at each articulation, as M. Decaisne found to be the case in Fiscum.* The parenchyma
between the vessels of the liber and wood is often dense, sometimes but rarely these vessels are seen to
be immediately in contact with the wood as at P late CV II./. 5 and 6 b. Wood. Within the bark are arranged
two concentric series of woody plates or wedges, these two series are separated by a zone of cellular substance, and
are generally arranged with tolerable precision : besides these the pith of the plant is intruded upon by other
wedges or bundles of vascular tissue, unsymmetricaUy disposed, one of them often occupying the axis itself. Each
wedge or plate is composed principaUy of concentric layers of very large vasa scalariformia, becoming more densely
packed and much smaller in diameter towards the axis of each layer, where they are almost invariably furnished with
a spiral filament. Between the layers of the first three or five years there is generally deposited two bundles of
pleurenchjTiia similar to that of the liber, one on each side (P late CVII. ter, f . 1 . / ) but between the more recent
layers there intervenes only the more delicate vascular tissue ( / . 1 and 2. e) : as mentioned above, however, pleurenchyma
is sometimes more copiously deposited between every layer, as at P late CVII. / . 5 and 6, b. The
narrow portion of each wedge invariably rests on a mass of pleurenchjina (P late CVII. ter, f . I. / ,) deposited at
the same time as the fibres of the liber c, that is during the first year, as in the common Misseltoe. The wedges of
wood belonging to the second series are smaller than those of the first, but similarly formed in all respects, and
consisting of as many layers, though the inner are very inconspicuous.
The pith consists of cellular tissue similar to that of the liber, and is very lax even in the older stems.
The transverse section of this stem, appears at first sight to differ very remarkably from that of most exogenous
plants ; this arises from the wood being deposited in two concentric series, separated by a broad zone of
parenchjTna, from the great breadth of the meduUary rays, the irregular distribution of the fibres of the liber
* Decaisne, Memoh-e sur le développement du Pollen &c. du Gui, in Act. Acad. Hoy. de Bruxelles, p. 49.
whicli ai-e sometimes biserial, and the disproportionate amount of sealarifonn tissue. The stmcture oiM.punctu-
lalum is however far more abnormal, fibres of pleurenchyma being deposited in the axis of the stem, thus replacing
the pith, and forming very obsolete rays, and aU futm-e increment of the stem being effected by an addition of
layers of variously marked scalariform tissue alone, as far as I have been able to observe.
Formation of wool. I shaU next describe the course the vascular tissue pursues in the newly formed buds
and branches, and thus attempt to explain the origin of the two series of woody plates which this species and
M. quadriforum DC. possess.
A transverse section of the stem of a flower- or leaf-bud made in the first year of its formation, (P late CVII.
bis, f . 10 and 1 1 ), presents a mass of globular utricles, covered with a delicate cuticle (a) formed of one moniliform
row of cells, and traversed by one series of twenty or thirty vascular bundles (i). These bundles descend from
the base of each leaf, traverse the branch and enter the stem. A transverse section of the stem again from which
the bud or branch is given off, and below the point of attacliment of the latter, presents two concentric series of
vascular bundles (CVII. Sm, / . 12. b,c), besides an imperfect tliii-d consisting of a few scattered promiscuously m
the axis of the stem ; the outer series rvas formed in the former, the inner is derived from the buds and branches
of tlie present year.
A longitudinal section through the axis of the stem, so made as to pass also through the axis of the branch,
clearly shews that it is due to the position in which the buds are developed that a second series of wedges of
wood is deposited. The buds originate towards the axis ot the stem, within the vascular bundles of the pi-erious
ycai-, (P late CVII. bis, f . 10. 4). and opposite the insertion of the petiole ( / ) . The whole of the vaseular tissue
descmding from a bud is consequently deposited within the wood of the former year ( /. 9 e.) generally each bundle
on entering the stem from the branch divides, one portion joining the old wood, the other, remaining free and
descending the stem, forms the second or inner plate of wood. Tlie com-se of the bundles is however very uncertain,
sometimes they do not divide, but either join the old vascular tissue, or continue free, and nt others one portion
crosses to the opposite side of the stem. Figures 9 and 10 of P late CVII. his, shew various modifications of the
com-se these vessels pm-sue, the uniform result being, that in the internode of the second year all the wedges of
wood are formed, though these become lower in tbe stem multiplied by dirision.
As each bud gives off thirty to forty bundles of vessels, and these being snperadded to those of the branch,
such a plexus ai-ises at the contracted junction of the second yeai-’s branch and that of the thii-d year that theh- course
can no longer be followed. Eacli of the woody plates however, continues to receive accessions tlu-oughout the life of
the plant, those of the inner series containing as many layers as those of the outer. I t is hence evident that the
bundles fii-st arranged in the branch of the second year ( / . 10 A), ou entering that of the third year ( / . 10, B),
must present a very complicated arrangement of tissues. The incrense of the stems in diameter being, however,
effected tlu-onghout the length of the plant by an addition of matter to the outside of both concentric series of
wedges, it follows that the growth is in one sense at the same time Exogenous and Endogenous.
However complicated the iiatm-e and disposition of these tissues may cause the developement of the stems to
appear, the order in ivhich each wedge of wood and its layers of pleurenchyma are deposited in the fii-st year is the
same as in Fisciuti ; nor are the tissues themselves very different from those of that plant. This is seen by comparing
the figure of a first year’s branch of Viscimi as given in M. Deeaisue’s elaborate essay* pi. iii. f. 4, or in Link’s
superb ‘ Icoiies’t pars iv. t. 8 . f 1, with that ot M. brachjstachjiun, (P late CVII. bis,f. 13).
Ill both ÌI. hrmiujsiiwhjiun and Viscum album two bundles of plem-enchyma are first deposited, one anterior and
* Link, leones sclcctæ .-Vnatomico-Botanictc.
t Liilk.l. 0. t. 8 . f.4. (3.