34 



SCIENCE. 



[N. S. Vol. XXIII. No. 575. 



DISCUSSION AND CORRESPONDENCE. 

 ISOLATION AND EVOLUTION. 



It seems to the writer to be a cause for con- 

 gratulation that a variety of possible factors 

 of evolution are being discussed at the present 

 time. Just as the factors associated with 

 Darwin's name together with those of the 

 Lamarckian school overshadowed all others in 

 the discussions of the last forty-five years, so 

 now we are in danger of having the ' mutation 

 theory' of de Vries obscure the botanical eye 

 to all other factors. Not that I would en- 

 deavor to throw any doubt upon de Vries's 

 facts; they are well authenticated. But they 

 do not, like the socialist's theory of political 

 economy, exclude every other factor from the 

 problem, and we should not, consciously or 

 unconsciously, so consider them. 



I have been greatly interested in President 

 Jordan's article on the part played by isola- 

 tion in evolution. While not disputing the 

 efficacy of isolation as a factor, I would long 

 hesitate to assign it the leading role to which 

 President Jordan assigns it. Professor Lloyd's 

 statement of the floral evidence against Jor- 

 dan's dictum is well put and timely, and 

 emphasizes a fact of distribution which is 

 well known to botanists. If it were necessary 

 to do so, the facts furnished by the distribu- 

 tion of the existing flora could be supple- 

 mented by paleobotanical evidence in so far 

 as facts of this nature are available. For 

 instance, during the mid-Cretaceous we have 

 a remarkable series of synchronous or nearly 

 synchronous* leaf-bearing strata outcropping 

 from the west coast of Greenland on the north, 

 through Marthas Vineyard, Long Island, 

 Staten Island, New Jersey, Delaware, Mary- 

 land and Alabama. These plant-beds have 

 yielded an abundant flora and each locality 

 furnishes a number of closely related species 

 which are largely identical throughout the 

 series. The following genera might be men- 

 tioned: Magnolia,, Liriodendron, Laurus, Sas- 

 safras, CinThainomum, Ficus, Aralia, etc. 



' The fact of correlation of the containing strata 

 is of no importance for the argument when each 

 outcrop furnishes several species which evidently 

 lived in the same habitat. 



Taking the genus Magnolia we have the fol- 

 lowing distribution of species in this region: 

 Greenland, four; Marthas Vineyard and Ala- 

 bama, five; Long Island, eight; Maryland, 

 three; Earitan formation (N. J.), eight; 

 Magothy formation (N. J.), three. In the 

 genus Ficus Greenland furnishes three species 

 and there are four species in each of the other 

 localities, with the exception of Marthas Vine- 

 yard. While in many cases leaf species may 

 be regarded as variations of a single actual 

 species, in numerous other instances we can 

 be sure that such was not the case. 



It would seem that isolation has not been a 

 primary factor to any large extent in specific 

 differentiation, but that it has operated in a 

 larger way in the development of generic or 

 even larger groups in isolated, particularly in 

 insular, regions. In other words, that it gives 

 a facies to the flora of any region. This is 

 implied in Professor Lloyd's article and is 

 merely the statement of a well-known fact of 

 observation. For instance, the Australian 

 region has a peculiar flora comparable to its 

 marsupial fauna, and it is difficult to imagine 

 that the facts are not explained in one case as 

 in the other by isolation. If we examine this 

 flora we flnd a number of characteristic types 

 of plant-life, the acacias, eucalypts, the many 

 Ehamnacese, Proteaceae, Santalaceae, Legu- 

 minosse, etc., the latest with over one thousand 

 species. In all these groups we find numerous 

 species, in many cases an excessive number, 

 closely related, and many with largely ident- 

 ical habitats, so that Professor Lloyd's con- 

 tention regarding distribution and specific dif- 

 ferentiation receives a large measure of 

 support. _ Edward W. Berry. 



Mabyland Geological Survey, 

 Baltimore, Md. 



on the human origin of the' small mounds 



op the lower MISSISSIPPI valley and TEXAS. 



The following extracts bearing on the the- 

 ory of the human origin of the small mounds 

 of the lower Mississippi Valley and Texas, 

 resuggested in a recent issue of Science by 

 Mr. D. I. Bushnell, Jr.,* may be of interest at 

 this time: 



•Vol. 22, pp. 712-714. 



