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882 COTYLEDON. 
edgings, marked with indentations and spines. 
The flowers are produced in scaly heads at the 
top of the stem, and they have a purple colour, 
and appear in July and August; and the seeds 
are oblong and angular, and are crowned with a 
hairy down, which wafts them far and wide upon 
even gentle breezes, and occasions the plant, if 
not kept down, to become a rapidly multiplying 
and exceedingly troublesome weed. ‘Twelve spe- 
cies have been introduced from foreign countries, 
chiefly countries bordering on the Mediterranean; 
but these species, though either curious or hand- 
some, are seldom to be seen in Britain except in 
botanic gardens. 
COTULA. See May-Wunp. 
COTYLEDON. A genus of plants. See Na- 
VELWORT. . 
COTYLEDON. The lobe or leaf of a seed. 
All plants which propagate themselves from 
spores or sporules, and have no seeds and conse- 
quently no cotyledons, are called in Jussieuan bo- 
tany acotyledonous; all which have one- lobed 
seeds are called monocotyledonous; all which 
have two-lobed seeds are called dicotyledonous; 
and all which have seeds with more than two 
lobes are called polycotyledonous. The acotyle- 
dons are very nearly coextensive with the cryp- 
togamia or agamous plants of the artificial sys- 
tems of botany, or with the cellulares or the en- 
dogens of the natural system ; and in consequence 
comprise all the groups whose means of propaga- 
tion are obscure, and whose general organization 
is comparatively simple. The seed of an ordi- 
nary monocotyledon is nearly cylindrical, with 
both ends obtuse, and has the axis of growth so 
completely in the interior as to be observable 
only when the seed is broken up or cut asunder ; 
the seed of a dicotyledon is very differently shaped 
in different plants, and has the axis of growth 
between its two lobes as between two planes, and 
allows this to be readily observed, and the lobes to 
be easily separated; and the seed of a polycoty- 
ledon has the lobes opposite to one another in 
a whorl ;—but polycotyledonous plants are so few 
in number as to be generally classed with the 
dicotyledonous plants. 
A cotyledon is a natural storage of nourish- 
ment for the developing embryo of a plant; and 
it feeds and nourishes the plantlet up to the stage 
of its acquiring organization and strength to 
draw sustenance from the juices of the soil and 
the gases of the atmosphere. It originally con- 
tains an excess of carbon; it afterwards imbibes 
oxygen, forms and discharges carbonic acid, and 
transmutes its starchy or highly carbonaceous 
matter into saccharine juices; and it sends off 
these juices into the nascent circulation, and for 
the initial sustenance of the plantlet. Some co- 
tyledons, especially those which contain a com- 
paratively large body of starchy matter, such as 
the acorn and the common pea, perform the 
whole of their functions under ground, and are 
thence designated hypogean; and others, espe- 
COUCH-GRASS. 
cially those which contain a comparatively small 
amount of starchy matter, such as the seeds of 
radishes and lupines, ascend rapidly on the plu- 
mule to the surface of the ground, there to as- 
sume the character of leaves, and to complete 
their functions by inhaling carbonic acid and 
fixing carbon, and are thence designated epigaan. 
COUCH-GRASS,—botanically Agropyrum re- 
pens. A most troublesome, vivacious, rapidly- 
spreading, perennial-rooted weed, of the field- 
wheat genus. Till Beauvois constituted the re- 
cent genus agropyrum, this plant was called 
Triticum repens; and even yet, it is very often 
thus designated. Six well-defined varieties of it 
grow wild in Britain,—the corn-field variety, 4. 
r, arvense; the subulate variety, A. 7. subulatum ; 
the thicket variety, A. 7. dumetorum; the capil- 
lary variety, A. 7. capillare ; Leers’s variety, A. 7. 
Leersianum ; and Vaillant’s variety, A.r. Vaillanti- 
anum, Hach of these has usually a height of about 
20 inches, and flowers in July and August. Three 
other grasses, also, of totally different genera, fre- 
quently share at once the name, the mischievous- 
ness, and the denunciation of couch-grass,—the 
creeping agrostis, or black twitch, Agrostis repens; 
the creeping-rooted soft-grass, Holcus mollis ; and 
the smooth-stalked meadow-grass, Poa pratensis. 
The field variety of creeping agropyrum, A. 7. 
arvense, however, is par excellence the couch-grass 
of arable land,—the abhorred and dreaded couch 
of the farmers of England, and the baffling and 
desolating quick-grass or scutch-grass of the hus- 
bandmen of Ireland. 
the British, field-wheat, from the resemblance 
which its young shoot or grassy blade presents 
to the young shoot of true wheat; and by the 
French, chiendent.or dog’s-tooth, either from the | 
outline of its shoot being somewhat like that of 
a canine tooth, or from the circumstance that 
dogs instinctively eat it to make them purge and 
vomit. Its root is creeping and jointed, grows with 
great rapidity, and sends up a new plant from 
every new joint which it acquires; its culm or 
seed-stem grows erect, but is not nearly so char- 
acteristic of the plant as the roots and shoots; 
and its seed-spike consists of a middle rachis and 
alternate floscules,—each of the latter, when the 
plant attains maturity, producing three or four 
chaff-protected seeds. On light and porous soils, 
the plant propagates itself with such prodigious 
rapidity by the roots, as speedily to overrun a 
whole field, and as to prevent its own culms from 
acquiring sufficient nourishment to mature the 
whole or even a considerable proportion of their 
seeds; but in very stiff soils, it makes compara- 
tively little way amidst the strong resistance of 
the firm land, and, in some instances, propagates 
itself not more rapidly by its roots than by its 
seeds. 
The existence or rather despotic usurpation of 
couch-grass on a farm, is as disgraceful to the 
tenant as the prevalence of docks or thistles; and 
when let in by a previous tenant, occasions enor- 
It is sometimes called, by | 
