ACQUIRED ADAPTATIONS 441 
he cannot make such a sequence adequately express his idea 
of their kinship. 
If we are warranted in supposing that all members of the 
crowfoot family are the descendants of plants like our marsh- 
marigold we may assume with scarcely less probability that 
plants closely similar to these primitive marsh-marigolds 
were the ancestors of all of the crowfoot order, and indeed 
that from plants having very much the same primitive 
characteristics came, in the course of geological ages, all of 
the dicotyls and perhaps all the monocotyls as well. Our 
mental images of ancestral forms are necessarily dim in pro- 
portion to the remoteness of the form conceived, and are 
likely to change as we receive new light. Yet these mental 
diagrams of things no longer to be seen help our seeing of 
the things about us. From the evolutionary point of view 
all life takes on a new significance. The possibility of gaining 
some glimpses of how the living world came to be as it is, 
makes all life more deeply interesting. Details of structure 
or behavior in a humble plant may lead us to some of the 
greatest truths of life. 
166. Acquired adaptations. The belief that all existing 
organisms are the more or less modified descendants of rel- 
atively primitive forms, is now as generally held by naturalists 
as is the belief in universal gravitation among astronomers. 
Yet astronomers are still striving to understand how it is 
that the force of gravity can act as it does; likewise naturalists 
‘are still debating the fundamental question as to how in- 
herited modifications have arisen. That somehow plants 
and animals have evolved is now taken for granted; but 
there are wide differences of opinion as to the way in which 
the changes have been wrought. 
In these few pages we can glance only briefly at the lead- 
ing views now held regarding the origin of species. Each 
theory aims to account for the appearance of those peculiari- 
ties of structure or behavior which distinguish one group 
from another; as for instance the climbing habit of clematis 
and the long, mostly hairy-tailed fruit which is found no- 
where else in the family except with certain anemonies in- 
habiting wind-swept fields. Peculiarities of this sort are 
