THE LIFE-FORMS. 355 



dominant and subordinate members, in socies, societies, and clans. The 

 abundant record of tree and shrub dominants must be taken as further proof 

 of well-developed grass consocies, even though there is almost no record of 

 these, just as they must also indicate the earher consocies of lichens, mosses, 

 and herbs. In the second case, the regular association of Phragmites, Sdrpus, 

 Typha, and Zizania in reed-swamps to-day carries with it the assumption that 

 they formed a similar consocies in the past. Thus, while Scir-pus and Typha 

 are first recorded from the Eocene, and Zizania has not yet been found as a 

 fossil, it seems clear that reed-swamps of essentially the same composition as 

 those of to-day date back to the Cretaceous, when Phragmites is first recorded. 

 Likewise, the existence of Quercus, Ceanothus, Rhus, and Prunus in the Cre- 

 taceous indicates the presence of their regular associates, Cercocarpus, Ardo- 

 staphylus, and Amelanchier, although these are not recorded before the Mio- 

 cene, Pleistocene, and Eocene respectively. Some, such as Symphoricarpus, 

 Fendlera, and Holodiscus, are not recorded at all, though the evidence from 

 phylogeny and association indicates that they must have evolved as early as 

 the Eocene at least. In the last case, the societies of the undergrowth of 

 maple-beech forest, for example, are probably indicated for the whole era by 

 those found in this climax to-day, and the same is probably true of all climaxes 

 that were differentiated early in the era. In the case of prairie-plains grass- 

 land, only a single dominant is recorded, namely, Stipa, from the Miocene of 

 Florissant. But it seems no more than fair to assume that Stipa was a domi- 

 nant then as now, that it was associated with Bouteloua, Agropyrum, Koeleria, 

 and other dominants, and accompanied by societies of Astragalus, Pentstemon, 

 Amorpha, Psoralea, Solidago, Aster, etc., as at present. 



Dominants. — ^The evidence from the record and from inference warrants 

 the assiunption that the majority of the dominant genera of present vegetation 

 had appeared in the Cretaceous period, and that practically all of them were 

 in existence as early as the Eocene. This is indicated by the fact that 11 of 

 the 14 dominant dicotyl trees are recorded for the Cretaceous, and the other 

 3 for the Eocene. If grasses and herbs had been as susceptible of fossilization 

 as woody plants, there seems no doubt that they would have left a similarly 

 satisfactory record in these two periods. This conclusion is supported by the 

 presence of Phragmites, Carex, and Cyperus in the Cretaceous, as well as by 

 that of Trapa in the Cretaceous and Polygonum in the Eocene, in addition 

 to the more primitive Ranales, AlismaUs, and Arales. The evidence for sub- 

 dominant shrubs is equally good, but for the herbaceous socies and societies, 

 especially of grassland, it is almost wholly inferential before the Miocene. It 

 is more difficult to determine the dominance of genera which have completely 

 disappeared from a region, such as Cinnamomum, Ficus, and Magnolia. 

 Their rdle in their present range furnishes one basis for inferring the degree 

 of dominance, and this is reinforced by the fact that the large nvunber of 

 species in each case clearly indicates a position in the climax or subclimax. 



Much emphasis has been placed upon the mixed character of the North 

 American forests, especially during the Cretaceous and the Eocene. Such 

 a conclusion is based too much upon the mere association of leaves in the 

 fossil horizons. It does not take sufficiently into account our greatly increased 

 knowledge of the differentiation of climates and hence of vegetation in all 

 geological periods, and whoUy ignores the significance of succession in the 



