434 KINSHIP AND ADAPTATION 



the different kinds of ]ilants that liave ever hved, we might 

 have a classification of tlie vegetable kingdom whicfi could 

 be represented diagrammaticallj^ by an enormous tree, made 

 up of innumeral)le segments wliich would correspond to 

 successive generations of species. The twigs of one branchlet 

 would stand for the species of a genus; the branchlets of a 

 minor branch for the genera of a familj^; while these minor 

 branches and those larger and larger would represent in turn 

 famihes, orders, classes, and, finally, the main l)ranches of 

 the kingdom. 



Let us suppose, now, that our evoh'ing tree of life as it 

 grew was gradually buried, all except the tips of the twig.g 

 which thus formed a flat top growing just above the surface 

 of the ground. Such a buried tree may show in a rough way 

 the nature of the facts presented to the evolutionist for inter- 

 pretation. Before him on the cartli are living species ar- 

 ranged in groups of groups accorchng to their various degrees 

 of resemblance. Below ground he may find a few more or 

 less fragmentary remains of creatures which liveil and died 

 in ages past. By their resemblances to forms still living he 

 is able to tell roughly to what brancli they may belong, and 

 if the extinct forms have peculiarities intermediate between 

 the characteristic features of living groups this would indicate 

 to him a kinship between these grouiis which he might not 

 have suspected. For example, certain coal plants, as Ave 

 shall see, which reseml>le t)oth ferns and gymnosperms led 

 botanists to recogniz(^ a njuch closer kinship between these 

 groups than tlic^ living forms had made a|)parent. 



But by far the greater part of the buried generations have 

 left no remains and may be reconstructed only conjecturally 

 by reasoning backward to the ancestral traits from the 

 pecuharities possessed in common by their supposed descend- 

 ants. Sometimes it has happened that striking confirma- 

 tion of such reasoning has lieen found. Thus, to take an 

 example from the animal Idngdom, zoologists were led to 

 believe from certain anatomical resemblances between birds 

 and re]3tiles that (liese groups wwr closely akin and must 

 have descended from a. t\pi' combining llie fundamental 

 characteristics of both; t!\en the r(.)ssil remains of a creature 



