124 SEAWEEDS 
The erect, green, assimilating shoots are, as has 
been indicated, very variously branched, and the 
species are classified mainly on the characters so 
displayed. They root in fine sand or mud, and 
commonly possess a creeping surculus or rhizome 
which gives off roots below and erect foliar shoots 
at intervals after the fashion of higher plants. The 
network of trabeculae or crogss-beams is very dense 
in most species, and traverses the cell-contents in all 
directions. They spring from the substance of the 
outer wall-membrane (Fig. 32, ¢ and d), and their 
principal function appears to be that of imparting 
support to the walls, though other functions have 
been speculatively ascribed to them without much 
show of reason. 
Dr. Correns has recently made a minute study! of 
the membrane, and has found that after treatment 
with sulphuric acid it has exhibited the formation of 
numerous sphzrocrystals, showing differences from 
those of cellulose demonstrated by Gilson and 
Biitschli. From the tests he has imposed, he has 
come to the conclusion that the membrane of Cawlerpa 
does not consist of cellulose in the narrow sense, but 
of a substance not yet fully known, and different 
from callus, fungus-cellulose, reserve-cellulose, ete. 
He has obtained similar results from two species of 
Bryopsis, and is inclined from this to regard with 
favour the view, otherwise vaguely indicated, of a 
relationship of this singular genus with Bryopsis. 
So little indication is there, however, of relation- 
ship with other Alge, that we have but the one fact 
1 Ber. Deutsch. Bot. Gesellsch., 1894, bd. xii., p. 355. 
