BOTANY. 
tion is so perfect and beautiful in the 
daphne laghetto, or lace bark of the West 
Indies, that it may be stretched laterally 
into a kind of gauze, sometimes used for 
articles of ornamental dress. The bark 
contains, in appropriate vessels, the princi- 
pal secreted fluids of trees in great perfec- 
tion. Its medicinal virtues in many in- 
stances are familiar to us; the Peruvian 
bark affords “ a cooling draught to the 
fevered lip while that of the cinnamon 
yields a rich cordial ; that whicji is stripped 
from the oak is used for the purpose of 
tanning, for which several other kinds are 
of inferior utility. When a wound is made 
in the bark it heals, though slowly, by the 
lateral extension of the portion which is left. 
Immediately under tire bark is situated 
the wood, which forms the great bulk of 
trees and shrubs. This also consists of nu- 
merous layers, as any one must have ob- 
served in the fir and many other trees. 
Each of these layers is moreover composed 
of other thinner ones ; their substance con- 
sists of innumerable woody fibres, and is 
perforated by longitudinal sap-vessels, va- 
riously constructed or arranged in different 
trees, and intermixed with other vessels 
containing secreted fluids or air. 
It would be superfluous to enlarge on the 
economical uses of wood in every country, 
fi'om the most barbarous to the most refin- 
ed. Of this material the savage forms his 
club and his spear, while the civilised part 
of mankind convert it to the purposes of 
comfort and luxury. Many conjectures 
have arisen among philosophers with respect 
to the manner in which the circular layers 
of wood are annually formed, and the effects 
which heat or cold may have on their for- 
mation. Cold seems to condense the opera- 
tion, as well as for a time to interrupt it ; 
since in the trees of hot countries these 
rings or layers are scarcely perceptible. In 
many trees more or less of the outermost 
layers continue for a time of a different 
colour and texture from the inner ones, and 
are called by workmen the sap. Such layers 
are unfit for any lasting service. The labur- 
num shews them very distinctly, and the 
oak likewise. It was long a matter of great 
uncertainty how, or whence each new layer 
of wood was added to the former ones. 
Malpighi and Grew, the first physiologists 
who gave attention to the subject, formed, 
without any mutual communication, an 
opinion, which proves to be correct, and 
to which we have already alluded, that the 
bark deposited every year from its own 
substance a new layer of wood. Hales 
thought this new layer proceeded from the 
wood of the former year; Linnaeus presum- 
ed that it was secreted, internally, next to 
the pith. The experiments of Duhamel 
and Hope confirmed the sentiments of 
Grew and Malpighi ; and at present there is 
no kind of doubt upon this subject. A layer 
of wood being formed every year, it is evi- 
dent that the age of a sound tree may be 
known from counting its rings when felled ; 
and it has been observed that hard winters 
are recorded in this natural register by cer- 
tain rings being more dense than the rest. 
In the north side of a tree also they are 
usually more narrow than on the south ; and 
upon this principle a mode for travellers to 
find their way through an unknow’n forest 
has been suggested, namely, that by felling a 
tree they might ascertain the points of the 
compass; but we humbly conceive that much 
more obvious means for the same purpose are 
within the reach of every traveller, and that 
the one recommended is somewhat like 
telling 
“ what hour of the day 
The clock doth strike by algebra.” 
Within the centre of the wood is the 
medulla, or pith, which is a cellular sub- 
stance, juicy when young, extending from 
the roots to the summits of the branches. 
In some plants, as grasses, it is hollow, 
merely lining the stem. Linnaeus believed 
this part to be analogous to the nerves of 
animals, and the immediate cause of the 
growth and evolution of all their parts ; that 
it was always struggling, as it were, to 
overcome the resistance of their woody sub- 
stance, and that it did accordingly elongate 
itself and cause the increase of the veget- 
able body in young and tender parts, where 
that resistance is least. The formation of 
seeds he conceived only put a final stop to 
its extension by the production of offspring 
from it. Facts are not wanting in support 
of this hypothesis; but there are many more 
conclusive ones against it. The real use and 
physiology of the part in question still 
remains in great obscurity. 
OF ROOTS. 
In defining the parts of vegetables it is 
found most commodious to begin from the 
bottom, proceeding upwards. Hence the 
root, which is the first part produced by a 
germinating embryo, comes first under con- 
sideration. Its presence seems necessary 
to plants, as it serves to fix and hold them 
