434 KINSHIP AND ADAPTATION 
the different kinds of plants that have ever lived, we might 
have a classification of the vegetable kingdom which could 
be represented diagrammatically by an enormous tree, made 
up of innumerable segments which 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 family; while these minor 
branches and those larger and larger would represent in turn 
families, orders, classes, and, finally, the main branches of 
the kingdom. 
Let us suppose, now, that our evolving tree of life as it 
grew was gradually buried, all except the tips of the twigs 
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 earth are living species ar- 
ranged in groups of groups according to their various degrees 
of resemblance. Below ground he may find a few more or 
less fragmentary remains of creatures which lived and died 
in ages past. By their resemblances to forms still living he 
is able to tell roughly to what branch 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 groups which he might not 
have suspected. For example, certain coal plants, as we 
shall see, which resemble both ferns and gymnosperms led 
botanists to recognize a much closer kinship between these 
groups than the living forms had made apparent. 
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 
peculiarities possessed in common by their supposed descend- 
ants. Sometimes it has happened that striking confirma- 
tion of such reasoning has been found. Thus, to take an 
example from the animal kingdom, zoélogists were led to 
believe from certain anatomical resemblances between birds 
and reptiles that these groups were closely akin and must 
have descended from a type combining the fundamental 
characteristics of both; then the fossil remains of a creature 
