THE MESOPHYTIC ERA. 



405 



Ginkgo, Laricopsis, Nageiopsis, Nilsonia, Pterophyllum, Zamites, etc., have 

 vanished completely or have disappeared from North America, except for 

 such corresponding genera as Abies, Dioon, Larix, and Zamia. The modern 

 genera Pinus, Sequoia, Taxodium, and Tumion were present, as well as Aralia, 

 Ficus, Populus, Sassafras, and Sterculia among flowering plants, and Asple- 

 nium, Dryopteris, Equisetum, Osmunda, Polypodium, and Selaginella among 

 fernworts. The records of angiosperms without exception are confined to 

 the Comanchean, though it seems certain that flowering plants will ultimately 

 be found in the Jurassic and late Triassic. A scrutiny of the "Tables of 

 Genera" (p. 245), however, will disclose the essential character of the Meso- 

 phytic flora. As is well known, the gymnosperms gave their impress to a 

 vegetation in which fernworts were becoming less and less abundant, and the 

 angiosperms were increasing from an unknown beginning in the middle of the 

 era to nearly complete dominance at its close. 



The methods of inference used in the preceding chapter are of little avail 

 here. This is primarily due to the fact that relationships are less certain, that 

 only a few of the fernworts and gymnosperms continued to the present and the 

 facts of association are hence less known, as well as to the poverty of the record 

 itself. Many of the genera are recorded for but a single period, and while it 

 seems plausible to assume their presence for at least a part of the period 

 preceding and following, this is obviously venturesome in an era of such great 

 changes. In some cases there is warrant from continuity for assuming the 

 presence of certain genera in periods where they are not recorded. Thus, 

 Cephalotaxopsis must have occurred in the Jurassic, since it is recorded in the 

 Triassic and Comanchean. This is true also of Cycadites and Dioonites, 

 and of Cycadinocarpus, which is found for the Triassic and Cretaceous. 

 Taxites and Tumion are recorded for the Jurassic and Cretaceous, but must also 

 have been present in the intermediate Comanchean. Similarly, Cunning- 

 hamites, Encephalartos, and Prepinus, which are recorded for the Cretaceous 

 alone, must have existed in the Mesophytic. 



Life-forms and dominants. — ^The record of thallophytic life-forms, with the 

 exception of marine algae, is of the scantiest. But it suffices to support the 

 inference that algse, fungi, liverworts, and mosses were in existence. Records 

 of algae and fungi from the Mesophytic are especially rare, but their occurrence 

 in the Paleophytic makes their existence in this era certain. Authentic lichens 

 are entirely unrecorded, and their occurrence must rest wholly upon inference 

 for the present. Liverworts are known for the Triassic, Jurassic, and Coman- 

 chean, and mosses more doubtfully for the Liassic and Stephanian. Charads 

 are known for the Jiu-assic and the Devonian, and must have furnished the 

 submerged form of the hydrosere throughout the Mesophytic. The role of 

 herbs must have been largely taken by fernworts, ferns such as Cheilanthites 

 and Selaginella perhaps taking part in the xerosere of rocks, as well as in the 

 layering of forests. Equisetum was almost certainly the dominant of swamps, 

 as is shown by its frequent behavior to-day. The absence of grasses is certain, 

 but their part may well have been taken by Equisetum on the one hand and by 

 geophilous cycads on the other, such as Zamia floridana to-day. Scrub 

 must have been constituted of cycadeans, and walchias and voltzias in par- 

 ticular, together with jimipers and yews, and tree ferns, Dicksonia, Dick- 

 soniopsis, etc. Of the tree-form there was no dearth of genera. Araucaria 



