138 THE JOURNAL OF BOTANY 
was made by means of series of microtome sections stained with 
Hoffmann’s Blue and supplemented by unstained a sections. 
Mature thallus.—The — thallus (fig. 1) can be divided 
oughly into owl zones: (1) The innermost, whisk consists of 
besigsteatiteally st ing filaments, meine es branching and having 
which are or three times as long as broad, and about three 
times as brad as the bers filaments. pes cells are joined 
end to end, so as to form irregular filamen atid: are connected 
m 
into a singh: nebwork by lateral projections “cere the cells. (3) An 
external zone of radiating mon ae filaments dichotomising 
repulaily towards the outside. The inner ‘cells of neighbouring 
filaments are joined by projections, so agen sc the cells a charac- 
teristic irreg shape. The outer cells of the filaments are 
closely adpressed to seer a limiting layer. None of these layers 
are sharply de limited fr om one another, oa like those 
The relative proportions of these layers vary according to the age 
of the tha e no gers of cells in the radiating filaments 
becoming proportionately much larger in the older parts of the 
thallus by remeneug from the | limiting layer which remains always 
meristema 
n none il the material examined by me was the thallus 
hollow. This does not, of course, exclude the possibility that 
other material might be found to be hollow, but one fact observed 
durin e cutting of the sections seems to suggest an explana- 
tion of the differences found in this respect. The central fila- 
ments form a very loose tissue, easily separable from the rest of 
the thallus, and when hand sections are cut the middle of them 
often drops out, thus giving the sections a spuriously hollow 
that the wall of all the cells consists of two parts: (1) an inner 
firm one which is nearly as thick in the central tissue as the 
lumen of the cells is broad, but is thinner in the outer; and (2) an 
outer very soft gelatinous part which is of very grea t thickness in 
the central tissue, but becomes less and less thick in * che interme- 
diate eo till in the limiting layer it is apparently absent. In 
airs.—On all ive of the re but especially in the 
younger parts, are found groups of hairs (figs. 2 and 3). These 
groups vary in size and frequency, but are in all cases so plentiful 
that it is difficult to see how they can have been overlooked by 
from Dictyosiphon i in aving n no hairs. These hairs have no con- 
ise close 
