STRUCTURE AND DEVELOPMENT OF SORANTHERA. 481 
Monterey, California, by Mr. W. R. Shaw, and sent by him to 
the British Museum. 
In young piants the thallus is composed of filaments which 
radiate from the base, the cells becoming smaller as they approach 
the outer surface, where they are free (Pl. 23. fig. 3). In very 
early stages these radiating filaments are closely packed together, 
but as the plant increases in size they become stretched gradually 
more and more apart and show an anastomosing tissue of cells, 
through which the original filaments can, however, be clearly traced 
(Pl. 23. fig. 4). The outer surface then consists of free 2- or 
3-celled assimilative filaments, the upper cell of which is some- 
what swollen (Pl. 23. fig. 7). These assimilative filaments re- 
semble those described and figured by Reinke in Chordaria 
(Algenflora der westlichen Ostsee, p. 75). When the stretching 
of the internal tissue has reached its limit, the cells become torn 
asunder, and by the time the plant attains to its full size there 
remains only a layer of polygonal cells 3-5 deep, which have 
almost a parenchymatous appearance. 
Meanwhile the outer surface has also undergone a change, and 
instead of the free assimilative filaments the thallus is enclosed 
by a continuous one-celled peripheral layer, as in Colpomen:a. 
Indeed the structure of the mature thallus of these two genera 
is so similar that it would be interesting to see if the resemblance 
exists also in young conditions. 
For some time it was difficult to trace the connecting links of 
this unusual alteration in the peripheral layer, and but for the 
presence in both stages of the typical rhizoids and the crypto- 
stomata characteristic of Soranthera, it might have been thought 
that the two plants were different species. However, at last a 
specimen was found in which the epidermal layer had evidently 
been just formed, and in many places single cells were still 
adhering outside it, showing the remains of the assimilative 
filaments (Pl. 23. fig. 5). These bad evidently been cast off, and 
the cells on which they had stood had become pressed together 
to form a continuous surface. Even after this fact was apparent, 
à reason for this unusual proceeding seemed far to seek. So far 
as I know, no member of the Pheophycee has first a surface of 
free assimilative filaments and later a compact, continuous 
epidermis. D. 
As regards the shedding of assimilative filaments, it is known 
that this takes place in Elachista scutulata before the formation 
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