GENERAL PRINCIPLES. 345 



mannii-Abies Insiocarpa-Pinus aristata. In some of the above cases the devel- 

 opment of a new climax is obviously the immediate result of sorting. The 

 more remote origins are due largely or chiefly to evolution, though it is clear 

 that evolution and sorting are both concerned in the production of most cli- 

 maxes. In the origin of the flora of a new era, evolution seems to have been 

 the primary process, though migration must have been an important factor. 

 In the adjustment of such a flora to climatic changes, the movement or sorting 

 due to migration was primary, and evolution consequent upon it. 



Recapitulation. — If the phylogeny of the community comprises the same 

 general process as that of the species, it should be recapitulated by the ontog- 

 eny as seen in the sere. In short, the stages of serai development which 

 reproduce the climax should correspond to the successive cHmax floras or 

 vegetations from the beginning of plant life on land down to the present. So 

 far as our present knowledge goes, the correspondence is so obvious that it 

 confirms the practice of morphology in using ontogeny to indicate the major 

 steps in descent. This principle is especially important in tracing the phylog- 

 eny of land vegetation, as the fossil record as known does not antedate the 

 Devonian. The relatively sudden appearance of an abundant and highly 

 developed land flora in this period can be explained only on the assumption 

 that land plants had existed during one or more if not all of the preceding 

 periods back as far as the Cambrian. There must have been herbaceous 

 fernworts, liverworts, lichens, and algae, nearly all of which were extremely 

 susceptible to complete destruction in the course of deposition. The assump- 

 tion of phylogeny that algae were the first water-plants is supported by early 

 geological evidence only to the extent of a relatively small number of marine 

 algse. The supposition that liverworts, and mosses also perhaps, were among 

 the earliest of land-plants rests chiefly upon present-day evidence as to their 

 r61e, smce no fossils of either are certainly known for the Paleophytic era. 

 The evidence of succession, however, affords strong support to the evidence 

 drawn from phylogeny, and the conclusion is irresistible that at least three 

 primitive land floras preceded that known for the Devonian. These were 

 (1) algse, (2) liverworts and probably mosses, and (3) herbaceous fernworts, 

 this being the essential order of succession in wet soils to-day. Under the 

 former assumption of equably warm and moist Paleophytic periods, these 

 must have represented a corresponding series of universal climaxes. With 

 our present knowledge of Paleophytic climates, it appears more probable that 

 there were cold or arid regions during the Cambrian and Silurian, which were 

 without vegetation or characterized by xerophytic colonies of Uchens, mosses 

 and fernworts. Hence it would seem that in pre-Devonian times there were 

 three successive climax periods. The algal climax must have been fairly 

 universal, but was perhaps differentiated into xeroid and hydroid areas, pre- 

 ceding a thalloid climax, in which liverworts and mosses represented the 

 hydrophytic climax, and lichens and mosses the xerophytic one. These must 

 have been followed by a similarly differentiated herb climax, composed of 

 fernworts. Even in the algal climax there must have been a sequence from 

 water forms to moist land or rock forms, such as Nostoc or Pleurococcus. The 

 development of a distinct sere with stages became possible, however, only 

 with the appearance of bryophytes and lichens, and was further emphasized 

 by the evolution of fernworts. At the beginning of the Devonian the prisere 



