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280
»corlical» and »epidermal» layers. The cutting off of the super-
fieial cells is seen in fig. 1 b. They form Ihe assimilatory layer
and have numerous disc-shaped chloroplasts, difficult to see in
preserved material, where all these cells are filled wilh a dark
brown substance. The stage seen in fig. 1 c seems to be the final
one as I do not believe that the wall surrounding the thallus cavity
increases much more in thickness. MITCHELL and WHITTING speak
of two epidermal layers, but I find only one.
Below the subepidermal layers the cells become larger and less
regular, forming a transition to the filamentous network of the
thallus; these cells stretch themselves, become separated and add
new elements to the large branched central filaments. Intercalary
divisions occur in this region (fig. 1 a). The last stage is reached
by the formation of innumerable hyphae. The interspace is filled
with mucilage.
According to MITCHELL and WHITTING the outer layers keep pace
with the inner ones through radial divisions. I do not believe that
radial divisions take place. If we study fig. 1 a and the figures of
RoE it will appear that in the young apex the filamentous structure
can be followed right through; the end cells have not originated by
radial divisions, but are branches from the supporting cell, and the
end cell often grows out to form a hair. The large central filaments
can be followed through the whole length of the thallus (fig. 2).
There seem to be several primary filaments, branching di- or
trichotomously. The same structure is repeated in the branches.
So far as I can see, the thallus has attained its definite thick-
ness a little below the apex, where the colour suddenly gets darker;
accordingly the apex is very broadly vaulted.
Thus, I conclude that Splachnidium is filamentous and the cortex
pseudoparenchymatous; the filaments are repeatedly branched and
may end in a hair of the Phaeosporean type, which is of short
duration. The end cells together form the meristematic zone and
build up the cortex by branching and dividing by cross walls; the
lower cells become elongated and give rise to medullary tissue.
This is an ectocarpoid structure, very different from the laminaroid
or fucaceous one, attributed to this plant by previous authors. We
find essentially the same structure in the Chordariaceae. It is to
be regretted that the earliest stages of the main shoots have not
been found, but with the facts at hand I feel justified in regarding
Splachnidium as a Chordariaceous type. The lower part of the hairs
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