Thalassiophyta and Algal Ancestry of Higher Plants 177 
direction may well have been taken at an early stage of trans¬ 
migration. Church is of the opinion that “the archegonium is a 
derivative only of a truly parenchymatous type of soma” (p. 13), 
but it may be doubted if that is necessarily the case. Ectocarpus 
shows us how a multiseptate reproductive organ can arise in forms 
which are in the main monosiphonous and it may be questioned as 
to how far such a multiseptate organ is really removed from a 
gametangium of Ulothrix or similar form where there is likewise 
division along several planes, although the resulting units do not 
become separated by walls. It is not difficult to suppose the gradual 
evolution of archegonia and antheridia from a gametangium pro¬ 
ducing a considerable number of gametes, by the gradual modification 
of those of the peripheral series into a protective cellular wall. But 
the matter cannot pass beyond the realms of pure speculation and 
it is possible to visualise a number of different possibilities. There 
do not however appear to be any grounds for assuming that even 
a very early prototype of these organs had been evolved prior to 
transmigration, although that may have been the case. 
Church regards the archegonium as being very probably poly- 
phyletic, a view with which one is inclined to sympathise. The 
regular occurrence of a ventral canal cell seems to me, however, to 
place considerable difficulties in the way of its adoption and to imply 
a common ancestry for all archegoniate forms. Such a feature is 
difficult to explain on a theory of convergence. In supporting a 
polyphyletic originTor the different groups of land-plants ( e.g . p. 82) 
Church places considerable weight on the type of flagellation of the 
spermatozoids. It may be doubted however if this feature always 
possesses the importance which is nowadays attributed to it, since 
several examples of the existence of diverse types of flagellation in 
one and the same form are known (cf. zoospores and spermatozoids 
of Vaucheria and the two forms of zoospores seen in some Saproleg- 
niaceae). We may not lose sight of the possibility that the type of 
flagellation may in part be related to external factors of which we 
at present have little comprehension. 
According to Church’s theory (p. 89) “The Algae of the trans¬ 
migration... combined the best features...of the known great con¬ 
ventional series of marine phytobenthon, and yet...belonged to none 
of them.” In other words the Algae that gave rise to the transmi¬ 
grants have completely disappeared. That is plausible, but it is 
difficult to understand on this basis why Green Algae (as we find 
them at the present day) should almost alone have adopted life in 
