16 MED 
of Irkutlk, on the Ilim : fixty-four miles Couth-weft of 
Orlenga. 
MEDVEZ'BI, five finall iflands of Ruffia, in the Frozen 
Sea : fixty miles from the mouth of the Kolima. Lat. 72. 
to 72.20.N. Ion.about 156. E. 
MEDVEZE'I, a cape on the north coaft of Nova Zembla. 
Eat. 77. 20. N. Ion. 68. 34.. E. 
M EDVE'ZI, a (mall ifland of Ruflia,in the fea of Ochotz, 
nt the mouth of the river Uda. Lat. 55. 10. to 55.16. N. 
Ion. 137. to 138. E. 
MEDUK'KA, a town of Arabia, in Yemen : thirty- 
fix miles fouth of Saade. 
MEDUL'LA, f. [Latin ] Marrow; the fat fnbftance 
that fills the cavity in the middle of a long bone. The 
white matter of the brain and nerves. See the article 
Anatomy, vol. i. 526, 593. and the word Marrow, 
vol. xiv. p. 415. 
Medulla, in botany, the pith of a vegetable; the in¬ 
ner veficular fubftance, or that which clothes the inner 
furface of a hollow trunk. The pith of plants is lodged 
in the centre or heart of the vegetable body, where it is 
as aftiduoufly protected as the brain and fpinal marrow of 
animals. In parts moft endued with life, like the root, 
or efpecially young growing (ferns or branches, the me¬ 
dulla is ufually of a pulpy fubftance; but tolerably firm, 
though rather brittle. Its colour is pale green or yellow- 
i(h, with a watery tranfparency, the fubftance being very 
juicy Its juices partake but little, or not at all, of the 
peculiar flavour of the plant, they being more of the na¬ 
ture of lap. Still there is no perceptible flowing from 
this part when wounded, at any time of the year, as far 
as we have obferved. In branches or ftems more advanced 
in growth, the medulla is found of a drier, more white, 
and evidently cellular, fubftance. (See the article Botany, 
vol. iii. p. 238, 9.) In this ftate it is known to every 
body in the full-grown branches of elder, and the ftems 
of rulhes. In thefe it is dry, highly cellular, fnow-white, 
extremely light and compreffible, though but flightly elaf- 
tic. Such are its different appearances, at different periods 
of growth, in many common ill rubs, as the currant-tree, 
lilac, mock-orange, hydrangea, &c. In the laft-mentioned 
ftirub, though nearly akin to the elder, as well as in the 
aucuba japonica, the pith is very abundant, and remains 
unufually long in its primary green juicy ftate. The pith 
of many annual Items, abundant and highly fucculent 
while they are growing, becomes little more than a web, 
lining the hollow of the adult Item, as in fome thirties. 
Many grades and umbelliferous plants, as the hemlock 
and chervil, have always hollow ftems, lined only with a 
thin fmooth coating of pith, exquifitely delicate and bril¬ 
liant in its appearance. The diltinrtion between a hollow 
(tern, only lined with medulla, and a folid one, entirely 
filled up with that fubftance, by no means indicates any 
material diderence between the plants fo circumftanced. 
Some fpecies of Hieracium have the one fort of Item, others 
the other; and this difference is often of ufe, for fpecific 
diftindlion, in that difficult genus. 
It is much eafier to defcribe the appearances of the 
medulla, which are few and but little varied, than it is to 
underftand the true nature, or phyfiology, of this part. 
There is fcarcely any concerning which a greater variety 
of opinions, or at lealt more oppofite ones, have been held. 
Du Hamel, an excellent obferver, though not always a 
correct theorift, confidered this part as not in any refpefl 
different from the reft of the cellular fubftance, difperfed 
through the vegetable body, and ferving to hold its dif¬ 
ferent parts together; nor did he attribute any particular 
function, in the vegetable economy, to any part of this 
fubftance. Linnaeus, on the contrary, thought the me¬ 
dulla the feat of life, and prime fource of vegetation. He 
conceived that its vigour was the main caufe of the pro- 
pulfion of the branches. His lively fancy formed to itfelf 
an idea of this organ altogether his own, as a living body 
of peculiar vivacity and energy, driving to enlarge itfelf 
in every dire&ion, and fucceeding belt where it found 
M E D 
leaft refiftance. Thu3 he explains the growth of plants, 
and efpecially of trees, at their extremities only ; the cor¬ 
tical fubftance, as he terms it, of the vegetable being, 
(confifting of its wood and bark, including the vafcular 
fyftem,) affording lefs refiftance where it is younger and 
thinner, while it derives energy itfelf from the powers of 
the fubftance it confines. His idea of the animal phyfio¬ 
logy was fimilar. He conceived the brain and nerves of 
animals to be analogous to the pith of plants; and that it 
was confined by their cortical fubftance, for fo he called 
their bones and mufcles, as the pith is by the more folid 
parts of plants. He thought he traced the origin of the 
ftamens, or male organs of vegetables, to their wood ; and 
that of the piftils, or female ones, to their pith. Hence 
he deduced a fine fanciful hypothefis, that the mule off- 
fpring of crofs impregnation (hould refemble its father in 
external habit and charafters, and its mother in internal 
qualities, which opinion he alfo extended to the animal 
creation ; nor did he want faffs to fupport it. Both king¬ 
doms were ranfacked to fupply them ; for fome faffs may 
be found to fupport any hypothefis, any at leaft conceived 
by a mind fo able, ingenious, and intelligent, as that of 
Linnaeus. In another office, which he attributed to the 
medulla, or pith, Linnaeus was unqueftionably miftaken. 
He thought it the origin of the wood ; believing that a 
layer was every year added internally to the body of a 
tree from this fubftance. Du Hamel refuted this opinion, 
by experiments, which clearly proved the wood to be de- 
pofited by the bark. 
But, while we thus rejeff opinions of the great Swedifh 
naturalift, which have been proved to want a folid foun¬ 
dation, it may be worth while to examine how far his 
general idea of the importance of the medulla may be 
defenfible. No one can deny that there is a great analogy 
between this part and the nervous fyftem of animals, with 
refpeft to fituation and proteftion, as well as in its gene¬ 
ral uniformity of appearance and texture in widely-diffe- 
rent orders of plants ; while the differences in thefe refpefis 
which it exhibits in other tribes, are not at all greater than 
thofe found in the nervous fyftem and brains of different 
claffes of the animal kingdom. If, moreover, it be faid, 
that the pith is of too Ample a conltruftion to allow a 
belief of its being of fo great importance to the vegetable 
conftitution as to be the feat of life, or immediate organ 
of vegetation ; furely vve are as little able to difcover any 
thing in the form or texture of the brain and nerves, to 
account for their wonderful but undeniable properties. 
Scarcely any phenomenon of the animal frame is lefs in¬ 
telligible, than the change in the pith of a plant from its 
fucculent ftate, to that dry congeries of an infinite num¬ 
ber of clofe cells or veficles, impervious to fluids, and 
having no communication with each other. 
The ingenious Mr. Knight has fuppofed the medulla 
to be a refervoir of moilture, to which the growing vege¬ 
table may have recourfe, when its fap-veflels are occafion- 
ally exhaufted by inordinate perfpiration. “ Plants,” fays 
this excellent writer, “ cannot, like animals, fly to the 
(hade and the brook.” This is undoubtedly true; but, 
inftead of fuch a refource, their leaves, when exhaufted, 
droop, or fold over each other,; fo that their pores are 
contrafted, and the very check which their energy receives 
prevents further exhaultion, and gives time for frefh fup- 
plies from the root. Mr. Knight has indeed (hown that 
the part in queftion may, occafionally at leaft, be difpenfed 
with, and removed from a branch without injuring it; 
but, on the other hand, he has more recently (hown the 
importance, if not of the medulla, of its analogous organ, 
the cellular fubftance; having found that fubftance capa¬ 
ble, as he thinks, of affuming the vafcular ftrufture, and 
aftual vegetation, of what Linnaeus terms the cortical 
fubftance of a plant. 
Dr. Smith, the learned and enlightened prefident of the 
Linnxan Society, is partial to the opinion of the medulla 
being, fome how or other, an organ fubfervient to the vital 
energy of the vegetable frame 3 but we can ftill lefs, if 
4 poffible. 
