326 
COMPOSITAE 
many cases, the stigmas curl so far back that they touch the pollen 
upon their own style, so that every fir. is certain to set seed, even 
though it be by self-fertilisation. In a few cases, eg. Senecio vul- 
garis, insect visitors are very rare, and the fir. depends entirely on 
self-fertilisation. The mechanism is about the simplest and most perfect 
that exists for attaining the desired ends. A striking contrast is seen 
in the orchids. Here we have bizarre flowers with most elaborate 
mechanisms, which yet so rarely effect their purpose that an enormous 
number of seeds have to be developed in every capsule; in the C. 
on the other hand, we have a simple mechanism, yet so effective 
that the number of seeds can be reduced to one. An interesting 
modification of the mechanism is found in Cynareae (see Centaurea) 
where the stamens are irritable. See also Artemisia (wind-fertilised). 
The involucral bracts, or ray-florets, or both, often close up over 
the central firs, in cold or wet weather, thus protecting the firs. 
Natural History of the Fruit. The ripening fruit-head is gene- 
rally protected from injury by the involucral bracts, which bend 
inwards over it, performing the function of a calyx. The calices 
of the individual firs, are thus rendered useless in this respect and are, 
in most C., used for purposes of distribution of the fruit. In the 
majority of cases, the calyx, after the fertilisation of the fir., grows 
into the familiar pappus, as seen in dandelions or thistles. This 
is usually composed of fine hairs, often branched, but in some cases, 
e.g. Achyrachaena, is leafy and membranous. The hairs are hygroscopic 
and spread out in dry air; this helps in many cases to lever the fruits 
off the receptacle. In Bidens and others the pappus is formed of 
stout barbed bristles, serving to cause the fruit to adhere to animals. 
In Arctium the involucral bracts become hooked at the tips and cling to 
animals. In Xanthium the receptacle is provided with hooks. In Sieges- 
beckia the bracts are sticky. A few genera, e.g. Helianthus, Beilis, &c., 
have no special arrangements at all, and the fruits remain upon the 
common receptacle till jerked off by wind or otherwise. [For other 
points and for details see genera, and Taliew in Bot . Cetitr . 63, 
p. 320.] 
General Considerations. The C. are generally regarded as occupy- 
ing the highest position in the Vegetable Kingdom, and are certainly 
about the most dominant and aggressive order that it contains. Some 
of the genera, e.g . Hieracium, vary so much as almost to defy classi- 
fication. The success of the order may be put down perhaps to the 
concurrence of several useful peculiarities, viz. 
(1) the massing of the firs, in heads, surrounded by involucral 
bracts : from this there results 
(a) greater conspicuousness, especially when ray-florets are 
developed; ( b ) a saving of material in the corollas, &c.; 
(c) the fact that one insect visitor may fertilise many firs, in a 
short time without having to fly from one to another : 
