THE DICOTYLEDONES 1941 



moths. The stigma is usually longer than the stamens, thereby preventing 

 self-pollination. 



Fig. 1869. — Leycesteria formoso. Raceme of 

 two-flowered cymes, with coloured bracts. 



The family is mainly found in northern latitudes, only a few species 

 being found in the southern hemisphere. Numerous leaf impressions of 

 Viburnum have been described from the Tertiary rocks of North America. 



ASTERALES 



The Asterales are the highest group of the Metachlamydeae, at least 

 from some evolutionary standpoints. The plants are almost all herbaceous 

 or slightly shrubby, very few are trees and many are annuals. The leaves 

 are very diverse in shape and are never associated with stipules. The 

 flowers are generally closely crowded together in heads or capitula sur- 

 rounded by involucral bracts. They are individually small and the anthers 

 are united to form a ring around the style. The ovary is inferior, bicar- 

 pellary but unilocular and with a single ovule, except in Valerianaceae 

 where there are three carpels, only one of which remains functional, and in 

 Adoxaceae, where there may be five. The embryo completely fills the seed 

 except in Adoxa, where there is endosperm present. 



As here treated the order contains four families, Adoxaceae, Valeri- 

 anaceae, Dipsacaceae and Compositae, but this treatment, while following 

 Hutchinson, differs from that of other authorities. Both Engler and Rendle 

 place the Compositae in the Campanulales while the Dipsacaceae, Valeri- 



