part 12] REVIEW OF PiLIOCEKE FLORA.8. 151 



Columns IV & V looked irregular, and 1 wondered whether much 

 reliance could be placed on my studies. To test the degree of 

 reliability, therefore, columns IV & V were plotted as a curve. 

 To my great amazement all the five loci lay along a regular 

 curve — the curve which shows the relation between the total 

 exotic element and the Chinese-North American part of it, through- 

 out the Pliocene and part of the Miocene (fig. 1). 



Before entering upon a discussion of the curve, and the deduc- 

 tions to be made therefrom, it must be stated that it is not an 

 absolute curve conveying an absolute truth, but a personal one of 

 which the truth is limited by the limitation of my knowledge of 

 the seeds of living plants, and by my judgment of the fossil species. 

 Inasmuch, however, as this personal bias holds throughout the 

 entire course of the investigation, it does not, 1 think, invalidate 

 the general conclusions, although it does perhaps modify them 

 slightly, in this way: — it will be noticed that (see Table, p. 149), 

 accordingly as the age of the deposit increases, the percentage of 

 selected (known) species decreases. The probability, almost the 

 certainty, is, that the unknown species are exotic, and that a large 

 proportion of them belong to the Chinese-North American associa- 

 tion. Seeing, however, that it is impossible to prove this, 1 have 

 had to exclude them. If they could have been included, the per- 

 centage of both elements (total exotics and Chinese-North American 

 exotics) in the table would have been increased ; and the increase 

 would have been proportionately greater going back in time. 

 This would not necessarily mean any change in the form of the 

 curve, but that each locus would be situate a little farther back, 

 and that the division between Pliocene and Miocene would also be 

 thrown farther back : that is, the proportion of the curve repre- 

 senting the Pliocene would be increased, that representing the 

 Miocene would be decreased. Such a change would imply that 

 floras of unknown age, in the Pliocene, would occupy a position 

 a little farther back in time than at present appears, and in the 

 Miocene, a little farther forward. 



Be this slight modification as it may, it may be conceded that 

 it is legitimate to draw certain deductions from the curve. 



(1) In the first place, I think that it may -be claimed that the study of 

 both living and fossil seeds is capable of leading- to reliable specific 

 determinations. 



(2) That the curve being based purely upon the study of fossil seeds 

 without reference either to palasozoology or stratigraphy, it shows that the 

 results arrived at by this study are in accord with those achieved by the sister 

 studies. Thus, granting that the loci of the Pont-de-Gail and Cromerian 

 floras represent fixed periods in time, namely the beginning and ending of the 

 Pliocene, then the position of the Teglian locux — that is, its position in time — 

 is in very accurate agreement witli that indicated by the palasozoological 

 study of tbe associated mammals towards the base of the Upper Pliocene. 

 Moreover, as will appear later, the indication given by the curve, that the exter- 

 mination of the Chinese-North American element in the West European flora 

 began in the Miocene, is also in accord with the results arrived at by strati- 

 graphy and pakBozoology. Consecpiently it may be claimed, that the study 

 of fossil seeds is able to furnish an instrument of equal delicacy and accuracj 



Q. .!.<;. S. No. 392. m 



