CHLOROPHYCEA 137 
atives of multinucleate plants. The British species 
are Bryopsis hypnoides and B. plumosa, Codiwm 
tomentosum, C. Bursa and C. adherens, and Derbesia 
tenwissima. 
UDOTEACEAE. 
General Characters. —The reproductive bodies 
(known only in the case of one genus, Halimeda) 
are zoospores produced within zoosporangia. It is 
not known whether they are zoospores or gametes in 
fact, since no observation has been made of their 
conjugation. The principal interest in the order is 
to be found in the vegetative part of the thallus, 
since the generic forms are not only of striking out- 
ward appearance, but of singular structure. The 
cohesion of the filaments composing the fronds is 
attained by their being interwoven (Avrainvillea), by 
incrustation of carbonate of lime (Penicillus and 
Halimeda), or by incrustation more or less partial 
with the addition of lateral haptera or holdfasts 
binding the filaments together (Udotea). 
The Thallus—In Avrainvillea (= Fradelia, Chloro- 
plegma, Rhipilia, Chlorodesmis) the frond is of simple 
structure, consisting of unicellular filaments, re- 
peatedly branched, and interwoven so as to forma 
stalked or sessile, fan-shaped, felt-like frond above 
and a dense mass of rhizoids below. The fan-like 
fronds are tough and spongy, and often lacerated at 
the edges. The filaments are dichotomously branched, 
and each branch is constricted at the base. In some 
of the species, the whole of the filament is constricted 
