68 o Blackman. — The Primitive Algae 
many unicellular naked brown Flagellates and some well 
defined colonial forms, of which we may mention three. 
Synura (Klebs (’ 93 ), Schmidle (’ 99 )) consists of a motile 
colony of about ten heart-shaped brown cells, each biciliate 
and grouped as in Pandorina , with an investing mucilage 
through which the cilia protrude. The cells are all naked 
and the colony is not a true coenobium, as it grows to mature 
size by division of its cells from a single free motile cell. 
Uroglena (Klebs (’ 92 ), Iwanoff (’ 99 )). The cells are of the 
same type, but the colony resembles Volvox in having a large 
hollow central space full of mucilage and a number of ciliate 
cells round the periphery ; but the colony may divide into 
two by constriction. On the phylum of brown organisms 
these colonial forms which resemble the Volvocaceous types 
of aggregation are found to be made up of true Flagellate 
cells, i. e. naked and dividing longitudinally, instead of true 
algal cells as on the green phylum. In spite of this, Butschli 
(’86) grouped these two families together in his Phytomastigoda. 
Hydrurus (Fig. 14, a , b , c), long thought to be a green Alga, 
was by Klebs (’ 93 ) shown to consist of a number of unciliated 
cells each with one phaeoplast and devoid of a cell-wall, but 
all imbedded in a branched cylindrical mucilaginous matrix 
which may be 30 cms. long and yet branches with a regularity 
rarely met with among the Algae 1 . The cells are single at 
the apices of the branches and form a peripheral layer lower 
down (< b ). The morphological differentiation of the branch- 
system found here, is unparalleled in such a loose aggregation 
of apparently unconnected cells: thus, the opposition of base 
and apex is very marked and the basal cells never give rise to 
branches ; the centrally situated cells seem to have lost the 
power of division, and growth in length is entirely conducted by 
the single apical cells, the branching being usually monopodial. 
Thus while the whole is clearly a colony of unicellular units, 
it has yet attained the morphological correlations of intimate 
multicellularity. The apical cells characteristically divide 
1 Phaeodermatium is generally held to be an unbranched cushion-like form of 
a Hydrurus colony. 
