THE PLANT RECORD. 291 



the present. They also afford a large number of criteria for evaluating the 

 evidence drawn from the plant deposits of the Cretaceous and the Paleozoic, 

 in which the facts are obscured by the conversion into coal. Indeed, the peat 

 deposits of to-day are but the existing representatives of a successional process 

 which has prevailed throughout geological time. Hence they possess the 

 unique value of enabling us in essence to investigate the past with the methods 

 and advantages of the present. 



Strates and stases. — From the standpoint of succession, the two kinds of 

 deposit mentioned above are so different in formation and value that it is 

 desirable, if not neceesasry, to distinguish them. In the one case, the plant 

 materials are carried away from the spot in which they grew, and are finally 

 laid down in sedimentary deposits as petrifactions, casts, impressions, etc. 

 During their transport by wind and water, the parts of different species, and 

 the species of different communities become greatly mixed and confused. 

 The fossil horizon thus formed furnishes fairly conclusive evidence as to the 

 flora, within certain limitations, but it yields Kttle or no direct evidence as to 

 the developmental relations of the vegetation. Inferential evidence may of 

 course occur in the greatest abimdance. It is clear, moreover, that the scat- 

 tering and mixing of leaves especially may vary widely. In the case of scrub 

 or woodland bordering quiet lakes or ponds, the number of leaves fossilized 

 as a consequence of falling into the water directly might have greatly exceeded 

 the number blown or washed in. Such an occiu-rence must have been excep- 

 tional, however, in view of the prevalence of wind and waves, to say nothing of 

 other disturbing factors. 



In the case of plants growing in water, or in swamps or bogs, each plant falls 

 where it grows, though of course some leaves and even small stems may be 

 whirled away by the wind or carried off by streams. The plants of the same 

 community remain together and are bm:ied more or less at the same time. 

 Moreover, they are preserved in correspondingly large number, as well as to 

 a remarkable degree, in consequence of the difl&culty of decay. As a result, 

 the successive populations or consocies are preserved more or less intact and 

 in their exact order, so that the reconstruction of the sere or cosere becomes 

 merely a matter of care and patience. It is these facts which make phjrto- 

 genous deposits in general and peat-bogs in particular, of such outstanding 

 importance in tracing the manner and course of succession in the past. 



The two deposits differ chiefly in two respects, namely, in the mixing of 

 plant parts from various soiu-ces, and in the degree of preservation. In the 

 one, the scattering and mixing by wind and water is a characteristic feature. 

 Hence, it is proposed to apply the term strate (Lat. stratiis, strewing, stratum, 

 bed, from sterno, spread out) to fossiliferous deposits of this kind. In the 

 phytogenous deposit, the water is stagnant, and the plant remains stay in 

 place. Accordingly, such a deposit may be called a stase (Gr. arcuTis, a standing 

 still; Lat. sto, stand). In the vast majority of cases, the strate and stase 

 are wholly distinct, and it is impossible to confuse them. Exceptionally, 

 however, as has been noted above, the fall of the leaves of riparian species 

 into still water may cause a strate to simulate a stase. Likewise, it must be 

 recognized that the leaves from an adjacent forest may be carried into a peat- 

 bog in large number, and thus affect the interpretation of the stase, as Steen- 

 strup (1842 : 19) long ago pointed out. 



