LIimEAN SOCIETT OF LOITDOJf. XIX 



either of the others. Some progress had been made in both direc- 

 tions. Sexual separation predominated, but not until some floral 

 development had taken place ; and neither had been carried to the 

 perfection exemplified ia the two great subclasses ; and the race would 

 probably have become long since extinct had it not been established 

 in a country which has apparently experienced since very early 

 times less of the vicissitudes affecting organic life than any other, 

 and had it not been at the same time endowed with other constitu- 

 tional peculiarities, enabling it better than any other plant to bear 

 with the physical conditions surrounding it. 



All this may be rejected as purely conjectural ; but surely Stras- 

 burger's genealogical tree is equally so. My object is merely to 

 show that the supposition that, of the three races now so distinct, 

 Welwitschia, after the first variations, has remained the least modi- 

 fied from the common stock, that the Conifers have undergone a 

 greater progressive change in one direction, and the higher Dicoty- 

 ledons a still greater advance in another direction, is more plausible 

 than the assertion that Conifers are the parent race from which 

 Gnetacese have directly descended, and that these, again, have en- 

 gendered the higher Dicotyledons. 



The establishment of direct pedigrees or genealogical trees, in 

 which the parent and descendant races are supposed to coexist in 

 the present day, is a favourite speculation of the German school, 

 especially since, after Hackel, it has adopted Darwinian views, car- 

 ried in many instances far beyond what is warranted by the works 

 of the great master himself. In plants at least, such pedigrees 

 appear to be wholly inadmissible, so long as we have no geological 

 record to justify them. If the image of a tree be really applied to 

 the illustration of the parentage of plant-races, it must be very dif- 

 ferently conceived. Taking, for instance, the Dicotyledonous class, 

 we might suppose a tree, in which the trunk represents the common 

 ancestor, forming in successive generations innumerable more or less 

 diverging branches, the greater part of which perish either imme- 

 diately or in the course of few or many generations, but some re- 

 main as branches or common trunks for future ramifications. We 

 may suppose the centre of the tree always to consist of those which 

 retain most of the ancestral characters, the lateral branches diverging 

 more and more as they have become more and more modified. These 

 modifications, even the extreme ones, may be for a long time very 

 slight ; but in the course of ages (as we may observe in varieties of 

 modern species) some of them may have acquired a more marked 



