TREE-ONION. 
it is evident, that, unless new species spring up 
spontaneously, no addition can by natural means 
be made to the original stock. Shrubs or young 
trees wafted from the European or American 
continents, would necessarily perish before arriv- 
ing upon our coasts; and the seeds of none of 
our present species of trees are fitted for long 
aerial voyages, and could scarcely arrive from 
the nearest point of Europe, even if whirled 
thence by a hurricane. As to the dissemination 
of trees by birds, no seeds of any kind, perhaps, 
have ever been found entire in the intestines, 
and the hardest are shattered by the least mus- 
cular gizzards. The present indigenous trees of 
the country are, therefore, very probably the 
species of which its ancient forests consisted. 
The principal, both in number of individuals 
and in economical value, are the Scotch pine, 
the common oak, the white birch, the dwarf 
birch, the alder, the aspen, the yew, the common 
ash, the wych elm, the bird cherry, the wild 
cherry or gean, the crab, the hawthorn, the 
blackthorn, the common mountain ash, the bas- 
tard mountain ash, the whitebeam, and the holly ; 
and a few of either the rarest as to individuals 
or the most doubtful as to true indigenousness, 
are the common elm, the beech, the white pop- 
lar, the black poplar, the common elder, the 
dwarf elder, the wayfaring tree, and the bullace- 
tree. 
TREE-CABBAGE. See Cappace. 
TRHE-MALLOW. See Lavatrra. 
TREE-OF-HEAVEN. See Arnanruus. 
TREE-OF-SADNESS. See Nycranruss. 
TREE-ONION,— botanically Adium prolife- 
rum. A curious, hardy, bulbous-rooted, white- 
flowered, perennial, herbaceous plant, of the 
garlic genus and asphodel family. It has com- 
monly a height of about 3 feet, and blooms from 
July till October, and is propagated from off- 
sets. 
TREFALLOW. Ploughing land the third 
time before sowing. 
TREFOIL,—botanically Trifolium. A genus 
of herbaceous plants, constituting the type of a 
sub-tribe of the lotus division of the leguminous 
order. ‘Twelve genera are comprised in this sub- 
tribe; and the chief of these are trifolium, 
medicago, lotus, melilotus, and trigonella. The 
flowers of the true trefoils are crowded in an 
elongated or globular spike or head; the petals 
generally remain attached when dry or withered ; 
the stamens amount to nine united and one soli- 
tary; and the pods in general are shorter than 
the calyx, and are either one or few seeded. Six- 
teen species grow wild in Britain; upwards of 
an hundred have been introduced from other 
countries; and about thirty unintroduced exotic 
species are known. All the species in Britain, 
exotic as well as indigenous, are hardy; about 
twenty are agricultural, and many of the others 
are ornamental ; about forty-eight are perennials, 
two are biennials, and all the rest are annuals; 
—_---—_—_—-—_-—-—-—— 
TREFOIL. 485 
several have a height of from 2 to 5 feet, a few 
have a height of only 3 or 4 inches, and most 
have a height of from 6 to 15 inches; a consi- 
derable number of both the perennials and the 
annuals are creeping or procumbent, and all the 
rest are erect. In one subgenus, consisting 
principally of annuals, and comprising one indi- 
genous species and about twenty introduced 
species, the flowers are spiked, the spikes have 
an oblong form and are ebracteate at the base, 
and the calyx is villous and is not inflated after 
blooming; in a second subgenus, consisting 
partly of biennials, much more of perennials, and 
still more of annuals, and comprising seven 
indigenous species, and somewhat upwards of 
forty introduced species, the flowers are capi- 
tate, the heads are ovate and often bracteate, 
and the calyx is villous and not inflated; in a 
third subgenus, consisting partly of perennials 
and partly of annuals, and comprising three 
indigens and about sixteen introduced species, 
the flowers are capitate and often deflexed, the 
heads are globose, and the calyx is not inflated ; 
in a fourth subgenus, consisting partly of per- 
ennials and partly of annuals, and comprising 
two indigens and six or seven introduced spe- 
cies, the flowers are densely capitate, and the 
upper lip of the calyx after the period of bloom- 
ing rises up in an inflated and arched manner 
and covers the legume; in a fifth subgenus, 
consisting principally of perennials, and compris- 
ing at least nine introduced species, the flowers 
are large, the petals are coriaceous and persis- 
tent, and the segments of the calyx are subulate 
or erect; and in a sixth subgenus, consisting 
principally of annuals, and comprising three in- 
digens and about ten introduced species, the 
flowers are capitate, the heads are pedunculated 
and ovate, and the petals are scarious, yellow, 
deflexed, and persistent. The principal agricul- 
tural species are fully noticed in the article 
Cuover; the species of the fifth subgenus are 
briefly noticed in the article LuprnastTER ; and 
the subject of the trifoliate plant which forms 
the national emblem of Ireland is discussed in 
the article SHamrRock. 
The indigenous species of the first subgenus 
is the field hare’s-foot, 7. arvense, an erect 
weedy annual of sandy fields, about a foot high, 
carrying flesh-coloured flowers in July and Au- 
gust. The seven indigens of the second sub- 
genus are the striated trefoil, 7. striatum, an 
erect weedy annual of barren grounds, about 5 
or 6 inches high, carrying purple flowers in 
June; the rough trefoil, 7. scabrum, a creeping 
handsome annual of sandy fields, about 5 or 6 
inches high, carrying white flowers in May and 
June; the starry trefoil, 7’. stellatum, a creeping 
handsome annual of the southern coasts of Eng- 
land, about 6 or 8 inches high, carrying purple 
flowers in July; the sea trefoil, 7. maritimum, 
an erect handsome annual of salt marshes, about 
6 inches high, carrying pale purple flowers in 
