[ i6 5 ] 
THALASSIOPHYTA AND THE ALGAL 
ANCESTRY OF THE HIGHER PLANTS 1 
By F. E. FRITSCH 
he publication by Church in 1919 of his “Thalassiophyta and 
X the Subaerial Transmigration 2 ” introduces in the main two new 
aspects in connection with the origin of land-plants. The first of these 
substitutes for the old view of invasion of the land via rivers and 
other pieces of freshwater, a conception of direct evolution from 
Seaweeds gradually becoming adapted to terrestrial conditions as 
they were left exposed on rising sea-bottom. The second hypothecates 
that the first land-plants originated, not from simple filamentous 
Algae, but from bulky Seaweeds of some considerable dimensions, 
exhibiting oogamy and fertilisation in situ and possessed of a regular 
alternation between an asexual diploid and a sexual haploid phase. 
Church’s fascinating memoir deals at great length with these two 
theories and all that they involve, and numerous facts are adduced 
in their support. At the same time it seems to me that not all the 
available ground has been explored and that, particularly as regards 
the second concept, there are certain facts which indicate the 
possibility of a different conclusion. 
It is generally agreed that the precursors of terrestrial plants 
must have been green, starch-producing Algae (cf. Church, loc. cit. 
p. 88), since other lines of Seaweeds possess a photosynthetic 
mechanism which does not appear to have been successful on land. 
Green Algae (apart from the highly specialised line of the Siphonales), 
however, play a relatively subordinate part in the sea, both as 
regards number of species and individuals. Moreover no Green Alga 
has attained to any really considerable dimensions or bulky paren¬ 
chymatous construction, and it is significant that in this respect 
there is nothing to choose between freshwater and marine Clado- 
phoraceae or Ulvaceae. In fact it may be said that Chlorophyceae 
as a whole possess no somatic organisation such as has been evolved 
1 From the Botanical Department, East London College, University of 
London. 
2 Oxford Botanical Memoirs, No. 3. 
