THILL-HORSE. 
to work him,—and to train him carefully and 
regularly up to the full stretch of his breathing 
powers, but not a jot beyond them, either in 
daily work or in daily exercise, so that he may 
acquire an increase of them by the force of habit. 
—The constitutional breathing action which the 
heavy draught horse has of a distinct and con- 
trasted nature from that of the racer or the 
hunter is sometimes, but improperly, called thick- 
wind. See the articles Horsz, Broxen-Wurnp, 
and PNEUMONIA. 
THILL-HORSE, or Tuitumr. The last horse 
of a team yoked in line-—the horse that goes be- 
tween the thills or shafts. 
THINNING. See Prantarion. 
THISTLE. A large group of composite-flow- 
ered, herbaceous plants, comprising many of the 
most common and troublesome weeds of agri- 
culture. The strictly proper thistles constitute 
the genus Carduus, and form the type of the 
suborder Carduaceze. This suborder is very ex- 
tensive, and comprises four divisions or tribes,— 
first, the true Carduacex, containing native and 
Jrajpontetl plants of at least 30 genera,—next, the 
Vernoniacee, containing plants of about 20 gen- 
era,—next, the Gnaphaliee, containing plants of 
about 15 genera,—and next, the Hchinopsidee, 
containing plants of about 13 or 14 genera. A 
large proportion of the true Carduacez either 
are popularly called thistles or may very readily 
be mistaken for them,—particularly all the spe- 
cies of the old genus Cnicus, and of the modern 
genera Carduus and Cirsium, and many or all of 
the species belonging to the genera described in 
our articles TuistLE (PLUME), CARLINE THISTLE, 
Corton-THistLe, Levzea,Saw-wort, RHAPONTICA, 
SrtyBum, and Cannsunea. Some plants also are 
popularly called thistles which do not belong to 
any division of the Carduaceous suborder,—par- 
ticularly those of the cichoraceous genus noticed 
in our article Sow-THIstLE. 
The strictly true thistle genus, Carduus, com- 
prises at present 3 indigenous species, aon 40 
introduced exotic species, and about 60 unintro- 
duced known exotic species ; ; and it formerly 
comprised some other species, both indigenous 
| and exotic, which are now assigned to the genera 
cirsium, serratula, and silybum. A few of the 
species in Britain have sessile or petiolated leaves, 
but the vast majority have decurrent leaves; 
some have an aggregate inflorescence, but a 
greater number have a subsolitary inflorescence! 
two or three have red or white flowers, and all 
the rest have purple flowers ; a few have a height 
of only from 6 to 20 inches, and a few are so high 
as 5 or 6 feet, but most have a height of from 2 
to 4 feet; about a dozen are annuals, and the 
rest are, in pretty equal proportions, biennials 
and perennials. The musk or nodding species, 
Carduus nutans, is an annual indigen of the grass 
lands of Been! about 2 feet high, with decur- 
rent leaves and ‘unpalle subsolitary dle) bloom- 
ing in July and August. The acanthus-like eee ee a 
THISTLE. 
cies, Carduus acanthoides, is an annual indigen of 
the waste grounds of Britain, about 2 feet high, 
with decurrent leaves and purple subsolitary 
flowers, blooming from June till August. The 
slender-flowered species, Carduus tenuiflorus, is an 
annual indigen of the hedge-banks and similar 
situations of Britain, about 2 feet high, with de- 
current leaves and purple aggregate flowers, 
blooming from June till August. 
The principal annual plants of the popular 
thistle group which infest the farm-lands of 
Britain are the three true thistles which we have 
just noticed, the common or potherb sow thistle, 
Sonchus oleraceus, and the centaury star-thistle, 
Centaurea calcitrapa,; the principal biennial ones 
are the welted, curled, or Virgin Mary’s thistle, 
Silybum marianum, the common carline-thistle, 
Carlina vulgaris, the marsh plume-thistle, C2r- 
sium palustre, the bull-thistle, spear-thistle, or 
common plume-thistle, Cirscwm lanceolatum, and 
the common cotton thistle, Onopordum acan- 
thium ; and the principal perennial ones are the 
corn- thistle, way-thistle, or common field plume- 
thistle, Cirsium arvense, the various-leaved plume- 
thistle, Cirsium Reeronh yllum, the meadow plume- 
thistle, Cirsium pratense, the common or corn- 
field sow-thistle, Sonchus arvensis, and the dwarf 
thistle or stemless plume-thistle, Cirsium acaule. 
Thistles are an exceedingly troublesome and 
destructive class of weeds; and they demand the 
sedulous care, not only of “adhonet | farmers, but 
of whole communities, for keeping them down 
and exterminating them. They tend to occupy 
an aggregately large area of cultivated land to 
the exclusion of useful plants; they appropriate 
a large amount of the nutrimental principles 
within the soil, to the starving of the crop or: 
the herbage amidst which they grow; they pre- 
sent so fierce an obstacle to the reapers of corn 
as to tempt them to grip and handle loosely the 
culms, and in consequence to leave a large 
amount of waste upon the field; they, in many 
instances, maintain so pertinacious a hold upon 
spots where they have taken root as to be very 
difficult of extermination; they, in all instances, 
so facilely and multitudinously scatter their 
winged downy seeds far and wide upon the wind 
that one free growth of them in a single nook of 
a district, or on a part of only one neglected 
road-side or one slovenly-managed farm would 
speedily propagate them over an area of many 
square miles; and wherever a rich lea soil, ca- 
pable of producing the most luxuriant crops of 
grain, is newly broken up, they so invariably and 
sometimes so profusely arise as to have given 
occasion to the adage for a blind man’s choosing 
land, “Tie me to a thistle.” A law exists in 
France obliging all farmers to free their lands 
from thistles at the proper season, and empower- 
ing any one to sue a neighbour who neglects this 
work, or to employ other people to do it at his 
expense; and a similar law in Britain, and in all 
other countries, would be of great econonieal value. 
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