ORIGIN OF LIFE, 75 
must, in each period, have given rise to innumerable 
multitudes of what have been called ‘trees of life,’ 
branching out into animal and vegetal forms of 
almost inconceivable variety. Myriads of these 
‘trees,’ including all their branches and innumerable 
ramifications, may have wholly died out during the 
many vicissitudes of the earth’s surface and the long 
lapse of ever fruitful ages; though the descendants 
or ultimate ramifications of some of such trees — 
dating back to quite different and perhaps far-distant 
epochs—may still survive. How far, however, the 
roots of any of the ‘trees’ from which the existing 
higher forms of life are derived, may have extended 
back into the depths of geologic time, we are utterly 
unable to estimate. 
Throughout all this life-evolving period of the 
history of our globe, the progress of ‘ organization’ 
seems to have been essentially similar. And that 
this should be so, seems readily explicable by the 
consideration that living things, both as regards their 
origin and their subsequent differentiation or develop- 
ment, are the immediate products of ever-acting 
natural laws or material properties. These properties 
should act therefore now as they have ever done, and 
so continue to produce almost similar effects. 
The lower the forms of life—that is, the nearer 
they are to their source—the greater seems to have 
