170 H. B. GUPPY^ M.B., F.K.S.E.^ ON PLANT-DISTEIBUTION 



the differentiating process following tl\e same lines at its early 

 stages in distant parts of the world is clearly indicated in these 

 conclusions, though it should be noted that this is not Mr. 

 Bentham's interpretation. Although admitting the very 

 ancient distribution over the world of the primitive stuck, this 

 botanist looked for the still earlier centre of dispersion, or, in 

 other words, for the home of the family. 



Xow, it is noteworthy that Professor Huxley, Mr. Darwin's 

 great lieutenant, in his remarkable paper on the Gentians 

 {Jour. Linn. Soc. Bot. xxiv, 18S8), wdiich as a display of method 

 may be regarded as a prophetic leap through two decades, 

 w^ould have nothing to do with centres of dispersion, or with 

 movements of migration in explaining the distribution of this 

 family. In two letters, giving some of his preliminary results, 

 which were written to Sir Joseph Hooker in September, 1886, 

 he says. . . . " It is clear that migration lielps nothing as 

 between the Old AVorld and Soutli American Florie. It is the 

 case of the tapirs (Andean and Sino-Malayan) over again" {Life 

 and Letters of T. H. Hnxiey, second edition, 1903, ii, 464-5). 

 His more matured opinions are given in his paper where he says 

 . . The facts of distribution of the Gentianecv . . . are 

 not to be accounted for by migration from any ' centre of 

 diffusion,' to which a locality can be assigned in the present 

 condition of the world," and he recurs again to the parallel case 

 of the tapirs, pointing out that with those animals " there have 

 been no migrations, but simply local modifications of the genus 

 at opposite ends of the primitive area, with extirpation in the 

 intermediate space." The species of the world-ranging family 

 of the Gentians fall, he says, into four groups, one primary and 

 " least differentiated," to whicli the South American, the Ant- 

 arctic, and the Arctic forms mostly belong, and the other three 

 groups " specialised " and comprising the species of the rest of the 

 northern hemisphere. There is, he remarks, " a strange general 

 parallelism witli the crayfishes " wdiich, thouuli widely distributed, 

 " become most differentiated " in the northern hemisphere. 



Like Mr. Bentliam with the Composite, Professor Huxley 

 regarded the Gentians as distributed over the world ages since, 

 and this is a most important point for our theory of differen- 

 tiation. The study of their means of dispersal would have been, 

 no doubt, characterised by him as interesting, but unimportant. 

 The existing Gentians he regarded as the relics of a widely 

 spread Tertiary Hora ranging over the two Americas and 

 Eurasia. Like Mr. Bcntham again, lie is able to dispense largely 

 with geological evidence, and, on a 'p'i'iori grounds, finds no 



