The Evolution of Plants. 
9 
On the broadest biological grounds, Mr. Church thinks the 
plant kingdom should be classified as follows:— 
.... ... ( Plankton. 
]. halassiophyta { Benthon 
Xerophyta - Xerophyton. 
Xerophyta include not merely land plants but all plants which 
have a “ water problem ” in their economy and all freshwater forms 
which have survived the subaerial transmigration, to grow as best 
they can in media other than that of the sea. 
Such, in very brief and incomplete outline, are some of the 
main features of Mr. Church’s story of the evolution of the leading 
series of plant life on the earth. The outstanding feature of the 
story is the insistence on the large marine algae as presenting us 
with various combinations of the factors, a selection of the best of 
which were employed in the adaptation to land life, and the corollary 
that only by a much more detailed and intensive study of seaweeds, 
can we obtain more positive knowledge of these factors. The 
characteristic merit of the author’s contribution to the subject, is 
his insistence on the widest possible outlook, on a broad 
consideration, in the light of all the known facts, physical, chemical 
and physiological, as well as structural, of the necessary conditions 
of evolution of land plants from water plants. There can be little 
question that our view-points in comparative morphology have been 
too narrow and academic, and it is all to the good to be taken into 
a freer atmosphere. The writer may be forgiven if he finds in the 
stimulating atmosphere of Mr. Church’s memoir one more 
evidence of the urgent necessity of escape from the bonds of our 
one-sided academic morphology in current teaching, and of laying 
far greater stress on a study of the physical and chemical conditions 
of life in its various forms. It is beside the point to reproach Mr. 
Church because he presents no new body of facts. He wants us 
to consider the facts we have in a saner manner, and to let the 
results of such consideration direct fresh research. Nor can we 
expect, as Mr. Church points out, to obtain fresh evidence on these 
points by searching for new fossils, exceedingly interesting as 
discoveries of new and simpler types of Pteridophytes, such as the 
recently described Rhynia, may be. It is overwhelmingly improbable 
that the original transmigrants which were the actual ancestors of 
our land flora have been preserved in fossiliferous rocks. We can 
only infer their characters, and that in the most general way, from 
a study of the structure and conditions of life of existing forms. 
