UMBRELLA-TREE. 
taken for one another by the ignorant—is that 
those species which inhabit watery sites are 
usually poisonous, and those which inhabit high 
dry sites are usually wholesome; and so much 
does this rule hold that it may possibly suggest 
some explanation why certain species which are 
poisonous in their wild state become wholesome 
by cultivation, and why certain other species, 
such as Ginanthe fistulosa and Ginanthe crocata, are 
violently poisonous in some districts and com- 
paratively or wholly innocuous in others. Two of 
the most remarkable instances of species which 
are poisonous in their wild state becoming whole- 
some and esculent by cultivation occur in the 
common celery and in Ginanthe pimpinelloides. 
Some of the most remarkable medicinal species 
are those which yield galbanum, opopanax, and 
asafoetida. Koch and Decandolle classify the 
Umbelliferze into three suborders, according tothe 
form of the seed. The smallest suborder, called 
Coilospermee, has channelled seeds, and comprises 
only one tribe, represented by the genus corian- 
drum ; the middle suborder, called Campylosper- 
mz, has curved seeds, and comprises three tribes, 
represented by the genera caucalis, scandix, and 
smyrnium ; and the largest suborder, called Or- 
thospermz, has straight seeds, and comprises 
eleven tribes, represented by the genera hydro- 
cotyle, sanicula, ammi, seseli, angelica, peuce- 
danum, tordylium, siler, cuminum, thapsia, and 
daucus. About a dozen hothouse species, up- 
wards of 50 greenhouse species, and between 500 
and 600 hardy species—nearly all herbs and be- 
longing to upwards of 100 genera—at present 
occur in the gardens and wilds of Britain. 
UMBILICUS. See Naventwort. 
UMBRELLA-TREE. Two ornamental exotic 
trees of about 30 or 35 feet in height,—the one 
the Magnolia tripetala, a hardy, deciduous, white- 
flowered native of North America,—and the 
other the Hibiscus guineensis, a tropical, ever- 
green, purple-flowered native of Western Africa. 
Both occur in British collections. 
UMBRELLA-WORT,—botanically Oxybaphus. 
A genus of curious exotic plants, of the order 
Nyctagineze. About a dozen species, varying in 
height from 1 foot to 6 or 8 feet,—some ever- 
green erect herbs, others evergreen trailers, and 
others deciduous trailers,—some hardy and others 
requiring a little protection,—most purple-flower- 
ed and blooming in July and August,—have been 
introduced to British collections from various 
parts of North America; and the greater num- 
ber love a soil of sandy peat, and require to be 
propagated from seed. 
UNDER-DRAINING. See Drarnine. 
UNDERWOOD. Shrubby, stunted, or coppice 
growths of forest trees,—either the literal ‘un- 
derwood’ of natural forests, or any kind of wood 
which is too small to be accounted timber. See 
the articles Coppice, Phanration, and 'Timper. 
_UNIOLA,—popularly Seaside-Oat. 
exotic grasses, of the fescue tribe. 
TV 
A genus of 
Four hardy 
URARIA. d45 
perennial species, two of them about 4 feet in 
height, the other two less than 1 foot in height, 
and all blooming toward the end of summer, have 
been introduced to British collections from North 
America; but they do not possess any agricul- 
tural interest. 
UNONA. A genus of ornamental, tropical, 
evergreen, ligneous plants, of the custard apple 
family. Nearly a dozen species, variously shrubs, 
climbers, and small trees, mostly brown-flowered, 
and all loving a soil of peaty loam, and propaga- 
ble from cuttings, have been introduced to 
British hothouses from India and Guiana; and 
about 30 more are known. Theesculent species, 
U. esculenta, a climber of 10 or 12 feet in height, 
introduced about 30 years ago from Madras, 
ranks in its native country as a fruit tree. 
UNSOUNDNKESS. See Sounpyzss. 
URANIA. A magnificent, evergreen, tropical 
plant, of the banana tribe. It naturally inhabits 
the sultriest forests of Madagascar; and was, a 
considerable time ago, introduced to British col- 
lections. It takes its name of urania, or “the 
heavenly plant,” from the stately grandeur of its 
appearance ; and it constitutes a genus of itself, 
and is specifically called speciosa or the showy. 
It attains a height of about 20 feet, and carries 
red flowers, and loves a soil of peaty loam, and is 
propagated from suckers. 
URANIUM. One of the rare metals. It was 
discovered in 1789 by Klaproth, in the mineral 
called pitchblende, which is a compound of pro- 
toxide of uranium and oxide of iron. Uranium 
does not naturally occur uncombined ; and 
though known to bea simple or elementary body, 
is not well understood in its detached state. The 
protoxide of it consists of one equivalent of the 
metal and one equivalent of oxygen, and has a 
very dark green colour, and most powerfully re- 
sists the action of heat, and forms green salts by 
combination with acids; and is employed in the 
arts for giving a black colour to porcelain. The 
peroxide of uranium consists of two equivalents 
of the metal and three equivalents of oxygen, 
and has a yellow or orange colour, and forms 
salts of a similar tint, and combines with alka- 
lies as well as with acids, and suffers permuta- 
tion into the protoxide by the action of strong 
heat, and is employed in the arts for giving an 
orange colour to porcelain. Sulphuret of uranium 
is formed by passing the vapour of bisulphuret of 
carbon over strongly heated protoxide of ura- 
nium, and has a dark grey colour, almost black, 
and suffers reconversion into the protoxide when 
heated in the open air. 
URARBIA. A genus of ornamental exotic plants, 
of the hedysarum division of the leguminous or- 
der. Six or seven species, varying in height 
from 14 to 8 feet, carrying either purple or lilac 
or pink flowers in the latter part of summer, all 
but one evergreen shrubs, some of them having 
pinnate leaves, two or three paired, and a termi- 
nating odd leaflet, others having trifoliate leaves, 
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