294 y ohnson. — Sphaerococcus coronopifolius , Stack A. 
applied to one another, side by side, so as to produce a com- 
pact cortex, the thickness of which is increased by the apical 
growth of these cortical secondary lateral branches (Fig. 7). 
Each member of the branch-system of the thallus thus con- 
sists of three layers ; a medulla formed by the central axis, 
a middle layer formed of the loose lateral cellular branches of 
the central axis, and a cortex formed as just described. The 
‘ midrib’ (central axis) and the £ lateral ribs’ (lateral cellular 
branches) were first observed and described by Sowerby, ac- 
cording to Harvey 1 , but their relation to one another and to 
the rest of the thallus in the way with which Schmitz 2 has 
made us familiar in the Florideae generally, was not known. 
Up to the present the central axis and its lateral branches 
have not been figured. Most of the figures of the thallus 
branches published are life-size, and taken from living or dried 
specimens. Examination however of spirit-material treated 
with clearing reagents and magnified four or five times 
brings out the central axis and its branches well (Figs. 1 
and 2). 
The Procarpium. 
As it is in the cylindrical filaments, the ultimate branches 
of the thallus, and in them only that the female sexual 
organs — the procarpia — occur, I shall speak of them as pro- 
car piiim-branches. It is no doubt in a great measure owing to 
the opacity of these branches, the absence of any external in- 
dication of the presence, not to say the exact position, of the 
buried procarpia, the smallness of the cells, and the number 
of different planes in which the various parts of the procarpium 
lie, that they have not hitherto been even mentioned. Their 
number somewhat atones for their general obscurity. We 
have seen that the whole margin of the thallus-branchlet is 
beset right and left with cylindrical filaments. These are all 
1 Harvey, Phycolog. Brit. ii. pp. 182-184, PL 61. 1846-1851. 
2 F. Schmitz, Untersuchungen iiber die Befruchtung der Florideen in Sitzungsber. 
d. k. Akad. d. Wiss. Berlin, 1883. Translation by W. S. Dallas, F.L.S., in Ann. 
Mag. Nat. Hist., vol. xiii. 1884, in which any following references will be found. 
