E. A. Neivell Arher — Hommomorphij in Fossil Plants. 387 



In a second paper,^ published in 1901, a further account was given 

 of very striking examples of parallelism of development among 

 these fossils, which has resulted in the production of homoeomorphs, 

 and of the phenomenon of homoeomorphy. Mr. Buckman has 

 further shown that " various species of different stocks may 

 either produce these developmental characters more or less con- 

 temporaneously, in which case such forms are called isochronous 

 homoeomorphs, or they may produce the characters at different 

 dates — a later form simulating an earlier one — in which case they 

 are called heterochronous homceomorphs." - The conception that 

 two genera of distinct ancestry may, by parallelism of development, 

 evolve a series of characters common to the two, which, as it were, 

 overshadow their distinctive and ancestral characters, throws a flood 

 of light upon difficulties such as those here described. 



Almost immediately after the publication of Mr. Buckman's first 

 paper, Messrs. Nicholson & Marr ^ showed that the same hypothesis 

 holds good for the Graptolites, and will " explain the more or less 

 simultaneous existence of forms possessing the same number of 

 stipes, but otherwise only distantly related, if we imagine them to 

 be the result of the variation of a number of different ancestral types 

 along similar lines." * 



This conception is, however, something more than a working 

 hypothesis, for both Mr. Buckman, in the case of Jurassic 

 Brachiopoda, and Messrs. Nicholson & Marr with regard to the 

 Graptolites, have been able to trace out the steps whereby two lines 

 of descent converge towards homoeomorphy, and the theory of 

 homoeomorphy has thus already won considerable acceptance. 



It has seemed to me that the hypothesis of homoeomorphy may be 

 of great service as a guide to the systematist in difficulties such as 

 I have just described among fossil plants, as it has been found to be 

 in other branches of palaeontology. In such genera as Neuropteris 

 and Linopteris some support may be found for such a view, but in 

 the present state of our knowledge of fossil plants I very much 

 doubt whether it is possible to demonstrate a series of intermediate 

 types similar to those brought forward in regard to the Brachiopoda 

 and Graptolites. It would, however, seem certain that if the 

 phenomenon of homoeomorphy is constantly borne in mind, that 

 many and excellent proofs will be obtained as our knowledge of 

 fossil plants increases. For the present, however, the theory as 

 applied to fossil plants must remain as little better than a working 

 hypothesis, the truth of which would seem to be exceedingly 

 probable. Even now we are not without evidence in support of 

 this view, for homoeomorphy is exceedingly common among living 

 plants. It is, of course, well known that many recent plants of 

 the most diverse origin show strong superficial resemblances. We 



1 S. S. Buckman, " Homajomorpliy among Jurassic Brachiopoda": Proc. 

 Cotteswold NaturaHsts' Field Club, vol. xiii (1901), p. 231. 



2 Buckman: ibid., pp. 232-3. 



3 jSTicholson & Marr, " Notes on the Phylogeny of the Graptolites " : Geol. 

 Mag., N.S., Dec. IV, Vol. II (1895), p. 529. 



* Ibid., p. 537. 



