189 
a new Genus of Endophytic Algae. 
stage in its development that the manner in which the mature 
frond is built up is easily observed. At first the thallus con- 
sists of rows of rose-coloured cells arranged in filaments which, 
by their excessive branching in one plane, form a network, and 
finally a more or less compact pseudo-parenchymatous 
membranous expansion, which being confined between 
the outer layers of the thick compound cell-wall of the 
Cladophora , and frequently entirely surrounding the cells 
of the host-plant, assumes, of course, the form of a hollow 
cylinder. 
On examining one of these strata it is at once obvious that 
it is composed of cells arranged in filaments of two sorts — the 
primary and the secondary filaments. The primary filaments 
are composed of long cylindrical cells, and extend straight 
forward for a considerable distance either singly or in close 
parallel rows of from % to 8 (usually 3 or 4) threads : not 
infrequently, however, after continuing in company for some 
distance, the filaments of which a group is composed 
separate again and diverge in opposite directions, each con- 
tinuing its course alone or joining with other filaments to 
form a new group. The very much and irregularly branched 
secondary filaments, on the other hand, are composed of short 
very variously shaped cells which arise laterally from the 
primary filaments. Where a number of primary threads run 
side by side in close proximity they form, as it were, one 
filament, the secondary branches arising only from those 
which form the border, and from that side of them which is 
not contiguous to the other filaments of the group : thus where 
five threads run in parallel rows the three middle ones are 
unbranched, lateral branches arising from the two outer ones 
on that side which is most removed from the centre (Fig. 6). 
As has already been stated these secondary filaments are 
always very much branched, and, continuing to send out 
branches, form, at the side of the primary filaments in the 
space which separates the isolated primary filaments or 
groups of filaments, an ever increasingly compact irregular 
network, and finally a more or less compact stratum of small 
