172 
F. E. Fritsch 
shallower. Assuming the rise to have been more or less continuous, 
however gradual, would the period of time elapsing between the 
establishment of a Benthos and the first emergence of land above 
the surface be anything like sufficient to suppose that the Benthic 
Seaweeds could have attained to the high stage of development that 
Church postulates? It seems improbable. 
Moreover, according to the geological testimony 1 there was no 
continuous ocean ab initio ; there always was land and apparently 
more of it than at the present day. That being so, there were probably, 
as in later geological epochs, frequent earth-movements leading, on 
the one hand, to subsidence of land and, on the other, to elevation 
of previously submerged sea-bottom. There may thus have been, 
always accepting Church’s theory as to the method of establishment 
of the land-flora, repeated transmigrations, some of which occurred 
at a much earlier epoch than others. It may, for example, be 
suggested that the Blue-green Algae, with their imperfect cytological 
differentiation, lack of a sexual process, and very simple morpho¬ 
logical construction, were transmigrants at an epoch when the 
evolution of algal life had not passed beyond this horizon. Their 
world-wide distribution is quite in accord with such a view. The 
Green Algae, already at a higher stage of development (complete 
cytological differentiation, sexuality, higher morphological con¬ 
struction), may have adopted terrestrial existence at a much later 
period, leaving only the siphoneous series to develop vigorously, 
mainly in the warmer seas. It may be freely granted that there are 
also possibilities of transmigrations at still later periods, the trans¬ 
migrants being highly organised Seaweeds as Church supposes. The 
considerations put forward in the preceding pages do not however 
appear to lend countenance to this view which moreover necessitates 
the assumption that at that far distant epoch evolution in Seaweeds 
had practically completed itself 2 and that there has been no appre¬ 
ciable change since. It may be questioned too whether such highly 
developed forms, as Church conceives the transmigrants to have 
been, would adapt themselves as readily to the conditions of a 
land-life as simpler Algae would. 
The changes involved in the assumption of a land-life are very 
fully considered by Church and, as regards the probable conditions 
1 Schuchert, loc. cit. p. 272. 
2 This is the view actually taken by Church, cf. p. 10. His reference to the 
Solenopovae of the Lower Carboniferous is scarcely relevant in this connection, 
since at that time the land-flora was already highly developed and we know 
little of the reproductive mechanism of these forms. 
