10 The Evolution of Plants' 
Once land plants were thoroughly established they must have 
acquired the general characters with which we are familiar, and 
the evidence of this or that variant on the type—one among 
thousands that must have existed—can tell us nothing significant 
about the general problem. 
There are some points in Mr. Church’s story that are doubtful 
or obscure. For instance he postulates a uniform ocean two miles 
deep on the surface of the earth as the medium in which the 
plankton phase of life was evolved and developed its perfection. 
The benthon age was made possible only by the approach of the 
sea bottom to the surface of the water as a preliminary to the 
emergence of continents. Geophysicists are not however agreed 
that this was the course of events. Some hold that there may 
have been land surfaces before the world was cool enough to 
support life. The “ orthodox ” biological view is that life arose in 
the warm water along the littoral and not as plankton in a 
uniform ocean. Unless we have a sound physical basis for the 
belief in the existence of a uniform ocean before land appeared 
the hypothesis of a plankton age preceding the benthon age is 
not necessary. Life may have originated as plankton, but we 
cannot be certain a priori that it did. There is also the question 
of the history of the content in mineral salts of the water of the 
primeval ocean. 
We shall be glad to publish criticisms or remarks on the 
subject of Mr. Church’s memoir, which raises, as was said at the 
outset, so many questions of the first biological interest. 
A. G. T. 
