Daisies and Thistles IQI 
corners of pastures, and sometimes the very centre 
thereof, we are almost sure to find the Black Knap- 
weed (Centaurea nigra), with its bristly, lance-shaped 
leaves and purple flowers. The name black Knapweed 
has reference to the almost black (dark-brown) hue 
of the comb-like margin to the bracts. Knapweed 
should be Knop- or Knob- weed, in allusion to the 
form of the involucre. In this species the outer 
series of florets is not always larger than the inner 
ones; but frequently these florets considerably exceed 
the stature of the others, and on examination they will 
be found to possess neither stamens nor pistil. In 
this genus the pollen-brush is not situated at the tips 
of the pistil arms, as in most of the Composites, but 
consists of a ring of hairs just below where these 
branch off. The anthers form a tube as usual, but 
the folded arms of the pistil are in the centre of that 
tube, and the pollen is shed in the space between the 
pistil and the anthers. If no insect-visitor arrives, 
the arms separate, and some of the pollen-grains fall 
upon the stigmatic surfaces, and self-fertilisation is 
effected. But these flowers are much visited by 
insects for the sake of their honey, and the probability 
that they will arrive before the stigmas are mature is 
very great. Miiller has observed no less than forty- 
eight different species of insects on the flowers of the 
Black Knapweed. The stamens are irritable, and if 
an insect only touches the tip of one of the anthers, 
contraction of the whole of the stamens takes place, 
which has the effect of so exposing the pollen that it 
is gradually removed by the under-sides of these 
visitors, who cross-fertilise older blossoms with it. 
Hardheads (C. scabiosa) is a larger, handsomer 
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