211 A. (". Anehvnoa — Tht Geological History of the 



The Composite favor the open spaces and rocky wastes of 

 the world and avoid the dense jungle and thicket growths. 



It seems permissible to infer that the ancestor of the com- 

 posites was a tree which possessed opposite leaves, pinnate or 

 compound, a compacted flower head possessing only disc florets 

 with free anthers, flowers regular, but the plant, possessing a 

 tendency early to xerophytisni somewhat similar in point of 

 time to that exhibited by the primary type of Acacia. These 

 plants flourished in the open places of the world, during the 

 Cretaceous. As the seas were drained off the lands, and as the 

 climate became differentiated the ancestral types forsook fhe 

 low tropical lands, because in the first place they were not 

 adapted to compete with the dense growths of the tropics, and 

 because the deserts in the tropics were too dry and hot for the 

 old lover of the well-watered but open spaces. As the lands 

 became isolated one from the other local differentiation ensued, 

 the old trees were weeded out in the north as the severe climatic 

 conditions of the late and post-Tertiary approached and vigor- 

 ous aggressive herbs were produced, which commenced to work 

 their way south along the mountains and high plateaus. 



The old tree Aster was among this group. In Australia the 

 arborescent form was reduced in size and a shrubby habit was 

 developed. From this the genus Olearia with 110 species in 

 Australia and Xew Zealand was derived. In South Africa 

 as in Australia, the old Aster had to face a gradual desiccation 

 of climate during the isolation of South Africa, and the shrubby 

 Felicia of 50 species was developed. In Chili, the old form 

 was modified to the arborescent Chiliotrichium, so also in the 

 Andes the arborescent genus Diplostephivm was formed, while 

 in St. Helena, the arborescent Commidendron and Melanoden- 

 dron are closely related to the old widely-diffused tree-Aster. 

 In the northern hemisphere the arborescent form was destroyed 

 and a vigorous aggressive and cold loving herb was produced 

 which worked its way south to the Equator in Africa. The 

 evolution of Bellis, Brachycome, Astranthium. Seubertia, 

 Garulewm, Keerlia, BeUium, Calotis, Minuria, and Yittndinia, 

 was somewhat similar to that of the asters, except that the 

 plants were herbs at an early stage during some differentiation 

 earlier than the Eocene, and that they are a decadent race, 

 except in Australia and the Mediterranean and, moreover, they 

 were not adapted to cold conditions so much as to barren, sandy, 

 and open conditions in climates not really cold. 



ecio, like the Aster, appears to have its primary form as 

 a tree, but it is a form which, like all other of the Composite, 



