4 
Review , 
overstimulates the formation of carbohydrate, which cannot be 
used in building new protoplasm because of the limited supply of 
the necessary food salts, and thus leads to the deposition of 
immense quantities of waste polysaccharide—a condition which 
reaches its extreme in tree trunks and in the thick walled tissue of 
xerophytes generally. The change to subaerial land life, in fact ? 
while immensely facilitating gaseous exchange 1 and therefore the 
constructive processes depending upon it, severely restricts the 
formation of new protoplasm, which can only be carried on by 
absorption of a great excess of water, so that the body of a land 
plant is much more largely composed of dead substance than is 
that of a submerged seaweed. 
“ The algae of the transmigration,” says the author, “ may he 
roughly visualised as having possessed the metabolic efficiency of 
the Chlorophyceae, the somatic equipment [parenchymatous 
structure and body segmentation] of the Phaeophyceae, and a 
reproductive scheme of life history more advanced than that of 
Dictyota , though in other respects falling behind that of the 
modern Florideae, in that these last have eliminated the flagellated 
zoid as microgamete in favour of a simple method of spermatogamy. 
The algae of the transmigration may be thus said to have combined 
the best features, as factors of the highest grade of progression, of 
the known great conventional series of marine phytobenthon, and yet 
to have belonged to none of them.” 
Mr. Church conceives of the condition for the evolution of 
such forms in the slow rise of the sea bottom to benthic conditions, 
i.e ., to within range of light penetrating from the surface. Thus 
emerges the conception of a benthic or seaweed epoch of the world’s 
history, which followed upon the earlier plankton epoch in which 
the ocean covered the surface of the globe to a uniform depth. 2 In 
the benthic epoch marine vegetation culminated in the shallow 
water areas of incipient continents. The marine benthon existing 
to-day, rich as it is in variety and development, is regarded as being 
a mere impoverished remnant of the benthic age, since it is 
confined to restricted portions of the very narrow littorals of the 
continents, and, together with the great bulk of the forms of the 
benthic age, the actual ancestors of the land plants have 
completely disappeared. 
1 Mr. Church is under the impression that the transmigrant to 
subaerial life is under worse conditions for obtaining carbon dioxide than a 
water plant. He seems to have got his data on the rate of diffusion wrong. 
2 That the ocean ever did so cover the globe must be regarded as 
questionable. 
