238 THE POPULAR SCIENCE MONTHLY. 



to exclude them. We see, from this manner of looking at things, 

 that the relations of the present arborescent species with those of 

 ancient ages are only the last consequence of a march or an an- 

 tagonism of long continuance, which must of necessity have left 

 traces. Regarding this closely, we find the indices of filiation of 

 the living by fossil species not wanting, but fully confirming our 

 interpretation ; and the genetic bonds disclose themselves to the 

 investigator from the moment when he consents to regard the 

 species as having acquired by degrees the characteristics which 

 it possesses, and also as susceptible of displacement by extension 

 or by crowding back. 



The morphological connection has certainly the signification 

 of a relationship ; but it can and must vary according as the rela- 

 tionshij^ is more intimate or remote, direct and immediate, or in- 

 direct and collateral. We can, by the aid of a direct method, 

 rather led by a kind of intuition than subjected to precise rules, 

 found a judgment concerning the bearing of these analogical 

 shades. While the opportunities of observing forms nearly allied 

 to those that are familiar to us diminish as we go back in the 

 past, yet, at whatever age we place ourselves, a near resemblance 

 always induces the notion of a direct descent of the recent form 

 from the one which predicted its traits in the midst of an order 

 of things remote from that which has since prevailed. The 

 observed resemblance may also be conceived to be the more de- 

 cisive as the species in which it appears belongs to a more ancient 

 period. The indices of genetic connection may thus go far back 

 into the past, and as to certain types of trees little subject to vari- 

 ance, they are discerned in a quite remote past. In order logically 

 to reach precise conclusions, he who engages in such researches 

 should take account not only of the type, but also of the species 

 considered in itself, that is, of the state of race, with its particular 

 history, of which it is sometimes possible to follow the incidents. 

 So far as is possible, the type, or union of allied forms, derived 

 originally from the same stock, should not be confounded with 

 the species, or the particularized race, which, its characteristics 

 having been once acquired and its aptitudes determined, necessa- 

 rily assumes a march in harmony with the tendencies that distin- 

 guish it, within an area suited to it. The plane-trees, poplars, 

 tulip-trees, beeches, and chestnuts appear toward the middle 

 of the Cretaceous period, but it does not follow that existing forms 

 are the immediate descendants of these primitive forms, or of any 

 one of them taken separately. The traces of our plane-trees, the 

 visible ancestor of the tulip-tree, and the evident predecessors of 

 existing poplars, make their first distinct appearance during the 

 Tertiary. So do those of the beech and chestnut, the introduc- 

 tion of which into Europe took place through isolated individu- 



