1 66 COMPOS1TAE 



of corolla-material, dvc. Throughout the fam., the same type of 

 mech. of the individual fi. is found, the differences being slight and 

 unimportant. It is simple, but effective. Honey is secreted by a 

 ring-shaped nectary round the base of the style, and protected from 

 rain and from short-lipped insects by the tube of the C. The depth 

 of the tube varies within fairly wide limits, but is never so small as 

 to permit the shortest-lipped insects to obtain the honey. As a fam., 

 the C. all belong to Miiller's fl. class B', but there is considerable 

 variety in the depth of tube, &c., and therefore also in the composition 

 of the group of visiting insects to each. Thus the long-tubed purple- 

 flowered Centaureas, &c. are mainly visited by bees and Lepidoptera, 

 while the short-tubed yellow Leontodons or white Achilleas are visited 

 mainly by flies. 



At the time when the fl. opens, the style, with its stigmas tightly 

 closed against one another, is comparatively short, reaching up to, or 

 projecting a small distance into, the anther tube. The pollen is shed 

 into this, and as the style grows it presses the pollen little by little 

 out at the upper end of the tube where it will come into contact with 

 visiting insects. At last the style itself emerges and the stigmas 

 separate. The fl. is now ? . Finally, in a great many cases, the 

 stigmas curl so far back that they touch the pollen upon their own 

 style, so that every fl. is certain to set seed, even though it be by self- 

 fert. In a few cases, e.g. Senecio vitlgaris, insect visitors are very 

 rare, and the fl. depends entirely on self-fert. The mech. is about 

 the simplest and most perfect that exists for attaining the desired 

 ends. A striking contrast is seen in the orchids ; they have bizarre 

 fls. with most elaborate mechs., and an enormous number of seeds in 

 every caps. An interesting modification of the mech. is found in 

 Cynareae (see Centaurea) where the sta. are irritable. See also 

 Artemisia (wind-fert.). 



The invol. bracts, or ray-florets, or both, often close up over the 

 central fls. in cold or wet weather, thus protecting the fls. 



Natural History of the Fruit. The ripening fr.-head is generally 

 protected from injury by the invol. bracts, whicli bend inwards over 

 it, performing the function of a K. The calices of the individual fls. 

 are thus rendered useless in this respect and are, in most C., used for 

 purposes of distr. of the fr. In most cases, the K, after the fert. 

 of the fl., grows into the familiar pappus, as seen in dandelions or 

 thistles, usu. composed of fine hairs, often branched, but in some 

 cases, e.g. Achyrachaena, leafy and membranous. The hairs are 

 hygroscopic and spread out in dry air; this often helps to lever the 

 fr. oft" the receptacle. In Adenostemma the pappus is sticky. In 

 Bidens and others the pappus is formed of stout barbed bristles ; the 

 fr. adheres to animals. In Arctium the invol. br. become hooked at 

 the tips and cling to animals. In Xanthium the recept. is provided 

 with hooks. In Siegesbeckia the bracts are sticky. A few genera, 

 e.g. Helianthus, Bellis, &c., have no special arrangements at all, and 

 the frs. remain upon the common receptacle till jerked off by wind or 

 otherwise. 



General Considerations. The C. are generally regarded as 

 occupying the highest position in the Veg. Kingdom. Their success 



