330 POPULAR FIELD BOTANY. 
so, not only from its form, but its colour, which contrasts so 
well with the ripe corn amongst which it grows. It stands 
two or three feet high, the stem and underside of the leaves 
covered with loose cottony down. ‘The leaves are long and 
narrow. Flowers large, handsome ; the centre floret small, 
and purple; those of the ray few, larger, spreading and of 
a beautiful blue colour. Scales of the involucre, or calyx, 
greenish ; the margins brown. 
CENTAUREA NIGRA. Black Knapweed. A common species 
in fields, with a curious involucre, each little scale being 
frmged with dark spreading teeth, like hairs, forming a 
beautiful object viewed through a glass. The florets are 
numerous, and purple. The plant is tall, being generally 
about three feet high; upper leaves long and narrow; lower 
toothed, and slightly divided. Cattle do not eat it. 
CENTAUREA SCABIOSA. (Greater Knapweed. Flowers 
much larger than the last, having a globular calyx with 
fringed scales ; but the hairs not so long; florets purple. 
and very numerous. Stem two or three feet high, erect, 
and much branched, leaves rather rough and divided, each 
part being long, narrow, and acute. 
