1956 A TEXTBOOK OF THEORETICAL BOTANY 



Anthers sagittate at the base. Style slender and papillose. 

 Fruit an akene, usually narrow or flat, sometimes with a slender 

 beak bearing a pappus which may have one or more rows of 

 simple or plumose bristles. Cichorium, Picris, Hieraciiim, 

 Leontodon, Taraxacum, Lactuca, Tragopogon, Scorzonera, Son- 

 clnis, Dendroseris, Fitchia, Lapsana, Hypochaeris and Rhagadiolus. 

 The plants are mostly herbaceous or occasionally shrubby. Trees 

 occur only in the isolated allied genera Fitchia (Polynesia) and 

 Dendroseris (Juan Fernandez). The species are widely distri- 

 buted, though mainly in the Old World with the chief regions of 

 concentration in the Mediterranean. Others are centred in 

 Western America and Mexico. There are a large number of 

 British species and many are cultivated either for their floral 

 eflect or as vegetables. We shall refer again to this tribe below. 



The presence or absence of laticiferous tissue is a valuable distinguishing 

 feature between the two main subdivisions of the Compositae and where it 

 is absent oil-glands are usually found. Inulin is present as a storage carbo- 

 hydrate in many genera, occurring either in root tubers, e.g.. Dahlia, or 

 in the rhizome, e.g., Helianthus tuberosiis. The anatomy is normal and 

 anomalous structures are rare. The plants are eflicient colonizers of new 

 ground and are often pioneers in vegetation, mainly because of the air-borne 

 fruits, the rapid germination and the very short life-cycle possessed by many 

 species. Groundsel is an excellent example of this. Moreover the fruit will 

 develop and ripen even after the plants are dead, a feature which can be well 

 observed among dried herbarium specimens, which though picked in 

 flower often bear mature seeds by the time they are dry enough to be 

 mounted. 



The condensation of the inflorescence to a capitulum represents a high, 

 if not the highest, expression of dicotyledonous development and it is 

 customary to consider the Compositae as the most advanced family of 

 the Dicotyledons. Despite this, geological evidence indicates that species 

 resembling those of the present day occurred in Tertiary rocks as far back 

 as the Oligocene, an early period for so advanced a family. 



The success of the Compositae in the vegetation of the world may be in 

 part, at least, attributed to the admirable adaptation of the flowers to cross- 

 pollination by a great variety of insects. Miiller points out that only the 

 Umbelliferae can compare with the Compositae in this respect, but that 

 whereas in the former family the nectar is exposed to rain on the epigynous 

 disc, the nectar in the Compositae is secreted at the base of a narrow tubular 

 corolla. Here it accumulates, rising up the tube as more is secreted. In 

 this way the type of insect which can obtain it will depend on the amount of 

 nectar secreted by each individual flower and the nature of the preceding 

 visitors. Hence it is a matter of chance whether the flowers will supply a 

 particular visitor and many insects visit and pollinate the flowers without 

 receiving any reward for their services. Observations show however that 



