368 
THE COTTAGE GARDENER AND COUNTRY GENTLEMAN, September 20, 1859. 
bi-pinnate, leaflets linear; flowers roundish, stalked, nodding; 
receptacle naked. 3 ft. Yellow. September. Austria. 
A. seeicea (silky-leaved). Stem adscending, rather branched; 
leaves covered with silky down; stem-leaves pinnate, leaflets 
tri-partite, linear-acuminate; bracts pinnated ; flowers globose, 
nodding. 2 ft. White. June. Siberia. 
A. Taurioa (Taurian). Stem erect; leaves hoary ; lower leaves 
bi-pinnate; upper leaves pinnate; leaflets linear-filiform; 
flowers oblong, sessile. 1 ft. White, green. July. Tauria. 
A.- vulgaris (Common). There is a variety of this 
with leaves white-spotted. It loses its character in fertile soil. 
A. Wuleenii (Wulfen’s). 1 ft. Yellow, green. July. Switzerland. 
This is a rather large genus with not very showy flowers. It 
contains the common Southernwood and Wormwood. I have 
selected a few of the best that are suitable for an extensive flower- 
garden border. Any common garden soil will suit them, and 
they are very hardy. 
Propagated by division of the plants in March or October 
in the usual way. 
ARUNDO-Reed. 
Nat. ord., Graminaceee. Linn. Triandria Digynia. 
Generic Character. — Glume naked, beardless, two-valved ; 
valves wrapping up the palese, which are two-bearded, and 
surrounded by bristles. Seed enclosed in the palese. 
Arundo donax (cultivated). Glumes three to six-flowered; 
florets as long as the glumes ; stem woody at the base. 10 ft. 
July. S. America. There is a variegated, or striped-leaved, 
variety of this, A. donax versicolor. This noble grass-like 
plant may be cultivated with good effect in masses in moist 
places. 
Propagated by parting the roots early in the spring before 
they commence growing. The stems die down in the autumn, 
and the stools require to be mulched over to protect them from 
the frosts. 
ASARUM—Asakabacca. 
Nat. ord., Aristolochiace®. Linn. Dodecandria Monogynia. 
Generic Character. — Calyx three or four-cleft, placed on the 
germ. Corolla none. Capsule coriaceous, crowned. 
Asarum ARIFOLIUM (Arum-leaved). Leaves sub-hastate, cordate; 
calyx tubular, shortly three-cleft. 1 ft. Brown. July. North 
America. 
A. Canadense (Canadian). Leaves kidney-shaped, mucronate. 
1 ft. Brown. June. Canada. 
A. Europium (European). Leaves kidney-shaped, obtuse, in 
pairs. 1 ft. Purple. May. England. 
A. grandifolium (large-leaved). This is the same as A. Cana- 
dense. 1 ft. Brown. May. N. America. 
A. Yirginicum (Virginian). Leaves cordate, blunt, smooth- 
stalked. These are veined and spotted on their upper surface, 
like Cyclamen autumnale. 1 ft. Brown. May. Virginia. 
The leaves of this genus are its greatest ornament; being ever 
green, they keep the borders furnished with foliage through 
winter. The flowers are very curious. They will thrive better if 
a little peat be added to the soil. 
Propagated by dividing the plants in March, and replanting 
the divisions immediately in fresh soil. T. Appleby. 
(To be continued .) 
THE SCIENCE OF GARDENING. 
(Continued from page 354.) 
Immediately beneath the bark is situated the wood, which forms 
the chief bulk of trees and shrubs. In all exogens it is formed of 
concentric layers, one of which at least is added annually. These 
layers are formed of a tissue of longitudinal fibres resembling 
network, the interstices of which are filled up with soluble 
matter, differing in each vegetable genus, but closely resembling 
its parenchyma. The layer immediately in contact with the 
bark is the softest and palest in colour, and thence is called the 
alburnum. It is in this that the vessels which convey the sap. 
from the roots to the leaves are chiefly situated. This layer is 
annually renewed, that of the previous year becoming more com¬ 
plete wood. Although the chief part of the sap-vessels, as just 
observed, is situated in the alburnum, yet others, though more 
scantily, are dispersed through other parts of the wood. Where- 
ever situated, they extend from the extremity of the minutest 
root to the leaves. 
In some trees, and especially in those which are not very hard, 
the line of demarcation of the wood and alburnum is hardly per¬ 
ceptible ; we see this in the Poplar, the Willow, the Chestnut 
the Bombax, &c.; on the contrary, in hard woods, this line is 
readily distinguished by the hardness and colour of the organs; 
thus, in the Ebony, the wood is, as every one knows, perfectly 
black, whilst the alburnum is white; in Cercis siliquastrum the 
wood is yellow and the alburnum white ; in Phillyrea the wood 
is brownish yellow, the alburnum white ; but in this last species 
the perfect wood is only found in very old trees ; and as many 
as fifty layers of the alburnum were remarked by De Candolle in 
Phillyreas about 200 years old. 
The relation of the thickness of the alburnum to the wood 
varies in different species and different individuals, not only from 
the preceding causes, but, moreover, from the age of the tree. 
Thus, the alburnum is equal to the wood in an oak six inches in 
diameter; it is as two to seven in a trunk of a foot; as one to 
nine in one of two feet, &c.; still these proportions given by 
Duhamel are very variable. Mustel has observed that different 
parts of the same layer of the alburnum may be transformed 
into perfect wood at different periods ; thus, he has Been some 
Oaks which had, on one side, fourteen layers of the alburnum, 
on the other, twenty; or, on one side seven, on the other twenty- 
two, &c. The layers of the alburnum are ahnost always thicker 
on the side where they are less numerous; that is to say, in other 
terms, that when a root meets a good stratum of earth, it 
nourishes the corresponding part of the tree more abundantly. 
Those parts which are most nourished have the woody layers 
thicker, and they arrive more quickly to the state of perfect 
wood, whilst the roots which fall in with poor strata badly 
nourish the corresponding parts ; and, consequently, these have 
the layers thinner, and they remain a longer time before they 
attain their complete hardness. 
All workmen know very well that the alburnum is less solid 
than the wood, and take care to separate it from the latter when 
they use it for building purposes, &c. Buffon, who performed 
with Duhamel some important experiments upon this subject, 
found that in the Oak the difference of solidity of the alburnum 
and the wood, is as six to seven. But the principal cause for 
which the alburnum is carefully rejected from the wood in 
building, is that on account of its looser tissue it is more liable 
than the latter to be affected by moisture, worms, and insects. 
We often find stakes placed in wet situations, with the alburnum 
either entirely decayed, or perceptibly changed, while the wood 
is still very sound.— (A. L)e Candolle's Organography). 
The idea that the annular layer of wood is rendered more 
dense and firm by severe winters is denied by reason, and de¬ 
monstrated to be false by actual observation. The layers are 
thickest on those sides of a tree where the largest roots and 
branches occur, and are throughout of a greater size in such 
years as afford the most genial period to vegetation. 
Each of the woody layers is, during its first year, a kind of 
very elongated cone, which surrounds the pith ; during the second 
year it forms a second cone, which surrounds the terminal pro¬ 
longation of the pith, and which is prolonged at the base in such 
a manner as to cover over the cone of the first year ; and thus 
cone after cone is formed in succession, until the destruction of 
the trunk. It evidently results from this, that each cone, or 
woody layer, only increases during the first year of its life; and 
that it is afterwards covered over by subsequent cones, and is, as 
it were, shut up by them in such a manner as not to be able to 
lengthen or thicken any more; it remains, after some years, in 
an almost passive state, and does not seem any longer to form 
part of the living organs of the plant. It results from this state 
of things, that the woody layers serve successively as coverings 
to each other; and if one of them has received any injury—as, 
by the action of frost, having letters cut in its tissue, or cavities 
hollowed out in its thickness, having nails driven into it, &c.—all 
these injuries, covered by subsequent layers, may be again found 
after any number of years; experiments have demonstrated this, 
and it serves to explain several facts to which marvellous ideas 
would be attached. Thus the layers of the alburnum, being full 
of sap, are liable to be frozen when the cold is very intense. 
When this accident takes place, and the frost does not reach the 
liber and the alburnum, the tree continues to live ; the frozen 
layer is covered over by a sound one—afterwards by several 
others; and thus covered, it is found in the centre of trees; this 
accident is named in French, Gelivure. We can, by counting 
the number of layers formed since the accident took place, know 
in what year it happened. Thus, in 1800, M. De Candolle had 
