F. E. Fritsch 
176 
Red Algae, a group so highly specialised that it may be doubted if it is 
warranted to draw any conclusions from them. On the other hand 
fertilisation in situ is a commonplace among freshwater Green Algae. 
Church lays great stress on the fact that a resting thick-walled 
oospore is unknown among marine Algae, as little as it is found 
among land-plants above the level of the Thallophyta, whilst the 
oospores and zygospores of freshwater Algae invariably become 
equipped with a thick coat and pass through a more or less prolonged 
resting period. This is certainly a significant feature, but perhaps too 
much importance may be attached to it. We have to suppose that 
the asexual reproductive cells gradually acquired these features 1 as 
they became developed as wind-borne spores, and if they underwent 
the change why not the zygote? It is at least plausible that a resting 
stage was temporarily adopted by the zygospores or oospores during 
transmigration and that, as the thallus became more massive and 
post-sexual nutrition was initiated, this stage was again lost. A 
parallel is furnished by the evolution of the seed among higher 
land-plants, where the presence of a megaspore-membrane in Cycads, 
Conifers, etc. cannot but be taken as evidence of the former existence 
of thick-walled spores which, as nutritive devices developed, re¬ 
mained in situ and lost the thick membrane. Whilst therefore there 
is no reason to suppose that the zygotes of Seaweeds ever presented 
a resting stage (the conditions of life rendering it unnecessary), it is 
quite possible that such was realised during transmigration and 
retained as an advantageous device by freshwater Algae liable to 
desiccation, though subsequently lost in the main lines of landward 
evolution. Transference of the resting stage to the asexual repro¬ 
ductive units would present little difficulty since many of the simpler 
Algae ( e.g . Ulothrix, Stigeoclonium) exhibit the power of initiating 
asexual resting cells side by side with the resting zygote. In fact 
the marked capacity for forming resting stages by several different 
methods (akinetes, aplanospores or encapsuled zoospores, zygotes) 
may have been another of the factors that led to the success of the 
green phylum. 
A necessary adjunct to a successful terrestrial existence was no 
doubt the development of a more perfect type of sexual organ such 
as is exemplified by the archegonia and antheridia of present-day 
Bryophyta and Pteridophyta, and the preliminary steps in this 
1 In this connection attention may be drawn to the facility with which most 
freshwater Algae adopt a thick-walled resting condition on the part of struc¬ 
tures that do not normally exhibit these features (akinetes, aplanospores, etc.). 
