Blackman and Tans ley. 
Pithopliora. Wittrock, 1877. 
Habit of Cladopliora. Zoospores not found. Repro¬ 
duction by akinetes. Exists only in fresh water. 
SrHAEROFLEACE/E. 
Filament unbranched, never attached. “Cells” very long 
with many nuclei. 
Reproduction by oogamy, many eggs being formed in 
each “cell.” Zoospores never formed by the “cells” of 
the thallus. 
Sphaeroplea. Agardh, 1824. 
“Cells” with nuclei and chloroplasts arranged in irregular 
rings separated by vacuoles. Nuclei 18—60. Any 
“ cell ” may become a gametangium without change of 
form. Antherozoids tapering, with two flagella, pene¬ 
trating the wall of the oogonium through round holes. 
Eggs spherical, with a colourless receptive spot The 
oospore germinates to form one or more bi-flagellate 
swarmers which elongate to tapering vegetative fila¬ 
ments without becoming attached. 
[This genus has so many unique characters that it stands quite 
isolated. The large number of nuclei in the cell is practically the only 
reason for its present position.] 
Series III. Ulvales. 
Thallus composed of uninucleate cells, parenchymatous, mem¬ 
branous, erect, and when young, attached atone point to the substratum 
by rhizoids. Chloroplast single, a parietal plate, or massive, filling 
most of the cell. 
Reproduction by bi- or quadri-flagellate zoospores and by bi- 
flagellate isoplanogametes, arising from unspecialised cells of the 
thallus. Zygote germinating at once ; embryonic forms various. 
Fam. I. Ulvace^e. 
Characters of the series.—All the forms are marine. 
Genera. 
1. Monostroma. Wittrock, 1866. 
Thallus at first a bladder and usually splitting later to 
an irregular foliaceous membrane which may float 
freely. Embryonic form a hollow sphere. Cells 
irregularly distributed in a single layer. Gametes 
and zoospores observed. 
2. Ulva. Wittrock, 1866. 
Thallus foliaceous, usually attached by a short stalk. 
Embryonic form a short filament which broadens out. 
Cells polygonal, in close contact, arranged in two 
definite layers. Gametes and zoospores observed. 
136 
5 - 
Earn. X. 
Genus. 
