#796.) 
layers are to be difcovered, nor central 
pith, nor medullary proceffes; the lig- 
neous fibres, placed by the fide of each 
other, are enveloppedin pith filling up the 
interftices; as they approach the cir- 
cumference, they are brought nearer to- 
gether, grow more compact, and, there- 
fore, are more flender : fo that the trunk 
is ftrenger, and more denfe, at its cir- 
cumference than its centre, directly con- 
trary, in this refpect, to the dicotyledo. 
nous plants. 
When a palm nut begins to vegetate, 
it throws out fuccellively, for the four 
-or five firft years, a number of leaves, 
which, by the union of their footitalks, 
form a bulb juft above the root fibres ; 
this bulb increafes, by degrees, in fize 
and folidity, and at length rifes through 
the ground, forming the trunk, being, at 
its firft appearance, 2s denfe and thick as 
it ever will be. ‘The figure, therefore, 
is that of an exact cylinder, whofe dia- 
meter is always the fame, though its 
axis is continually increafing. 
It happens, however, fometimes, that 
the trunk does not preferve a regular 
cylinder throughout: this: irregularity 
takes place on account of the greater or 
Je{s abforption of nutrition by the roots ; 
thus, if a young plant be moved from a 
very dry to a moift fituation, the nutri- 
tive juices being more abundant, the up- 
per part of the trunk will be thicker 
than the lower, and vice verfa. Of this 
variation, a cycas, in the National Gar- 
den, furnifhes a remarkable exaimple. 
This plant was tranfplanted from the 
dfle of France, in’ a tub, in the year 
z7893; when arrived at Paris, it lan- 
guifhed for a long time, during which its 
ftem, however, increafed in. length afew 
inches’; but the whole of this elongation 
was much lefs in diameter than the reft 
of the trunk. By flow degree, the tree 
recovered ; the fhoots became more vi- 
gorous and larger, but the ftrangulated 
part continued, and ftill continues, of its 
former dimenfions. That portion of 
trunk which was produced in its na-: 
tive country, is 23 inches in circumfe- 
rence, the ftrangulated part 14 inches ; 
the upper part is 19 inches, and the in- 
feriority in fize of this, to the lower 
part of the flem, may be fairly attribut- 
ed to the deteriorating influence of a fo- 
reign climate. The fame caufe could 
never produce the fame effect in a tree 
with two feminal /eaves, becaule, its in- 
creafe in bulk being owing to the fuc- 
‘eflive. application of concentric eylin- 
oders, extending from its bafe to its fum- 
Mouocotyledonous and Dicotyledonous Vegetables. 
877 
mit, it preferves its original form and 
proportions, whether the new cylinder 
of wood be greater or lefs. it has been 
mentioned, in the former part of this 
paper, that the zmzer bark of bicotyledo- 
nous trees is renewed every f{pring, and, 
therefore, that the number of concentric 
cylinders is greateft at the foot of the 
tree, the branches of a year’s growth 
poffeffing only a fingle layer of wood. 
Nothing fimilar takes place, with re- 
{pect to the bark of the palm, that being 
merely an expanfion of the fibres at the 
bafe of the leaf-ftalks, covering the 
trunk with a coarfe imbricated kind of 
net-work, eafily detached, and not ca- 
pable of being renewed. 
2. CANEs. Canes bear fo near a re- 
femblance, in their ftruéture, to palms, 
that it is not eafy to form diftinétive cha- 
racters between them. A longitudinal 
fe€tion of the common cane will at once 
fhow the refemblance, and aimoft iden- 
tity of conformation ; the central fibres 
are fo loofely difpofed, that the naked 
eye may, with eate, diftinguifh the in- 
tervals, and air or {moke may be, with- 
out difficulty, paffed through a ftem of 
feveral feet. The fibres approach each 
other very fenfibly, as they recede from 
the centre, and neither concentric cylin- 
ders, nor medullary proceffes, can be dif- 
covered. 
3. Grasses. The fame appearances 
occur in the ftruéture of all fuch grami- 
yaceous plants as have perennial ftems, 
fuch as arundo bambos (bamboo) arun- 
do denax, panicum arboreum, panicum 
latifolium, faccharum officin. ({ugar- 
cane) and many other fpecies of this 
numerous tribe. The veffels are ar- 
ranged parallel to each cther, without 
forming concentric cylinders ; the pith, . 
or medullary fubftance, 1s diftributed in 
the {mall intervals between the fibres, 
which, as they approach the circumfe- 
rence, become more, flender and com- 
pact, without any traces of medullary 
procefles. But if the grafles are con- 
nected with the palms and canes, by the 
great diftinctive charaéters of monocoty- 
ledonous plants, they yet differ in feve- 
ral particulars which ought to be men- 
tioned. The ftem is hollow, and divided 
by knots placed at regular diftances, 
which form tran{verfe valves in the in- 
terior of the ftem, contribute to its 
ftrength, and produce leaves and roots. 
The leaves are always fimple, embracing 
the ftalk ; and, inftead of being folded 
in two, like the leaves of the palm be- 
fore expanfion, they are rolled inward 
sky fron, 
