CLARKE— THE AGE OF THE EARTH. 279 



" the marine organism was brought into direct association with atmos- 

 pheric air and subaerial environment to mark out new lines of pro- 

 gression to still higher and more strenuous forms of land life, though 

 these are again necessarily expressed in terms of preceding organiza- 

 tion and mechanism." The point to be made here is that with the 

 earliest lifting of land from the sea, benthic algae of advanced struc- 

 ture, "the remarkable algae of transmigration," as he has character- 

 ized them, got their foothold on the land. " The Evolution of the 

 Land Flora was a phase of transmigration in situ" and did not 

 involve a preliminary landward migration by the way of fresh water, 

 " the biological factors being exposure to more or less desiccation and 

 the removal of the food solution." " The few races that survived 

 only did so by pressing to the utmost any principles of economy in 

 reproductive output that they may have previously initiated," such as 

 oogamy and fertilization in situ. 



The picture presented by this line of carefully founded reasoning 

 is even more impressive in its demands upon time than the argument 

 we have presented from animal life. It is summed up thus : Plants 

 of complex organization and function — deductively of higher organ- 

 ization than can be to-day found among the algae — had worked out 

 their attainments before their arrival on the land, and probably this 

 organic achievement, not surpassed in the seas of to-day, was accom- 

 plished at a stage in earth history long before the Cambrian Epoch 

 brought with it the tangible evidence of the complex animals. The 

 argument from the plants is more highly deductive than that from 

 animals, but its steps are logically taken from effect to cause, and in 

 its presence we must stand uncovered at the inconceivable lapses of 

 earth-time through which these transmigrant plants were slowly work- 

 ing out their organization in the waters when there was no permanent 

 land — a period of time which must have been longer than all time 

 that has passed since the emergence of the Laurentian or the basal 

 rock complex of the great shields of the earth. 



II. 



If we are prepared to concede the steadily increasing weight of 

 evidence of the polyphyletic origin of genera which recent researches 



PROC. AMEK. PHIL. SOC. , VOL. LXl, T, JAN. 3, I923. 



