200 
by horizontal walls, the sorus will finally be placed in a groove in the frond (fig. 119 C, 
comp. Heypricu |. c. Fig. 3). When rising later it takes a more superficial position. 
The other specimens arise from disc-shaped ones by very strong enlargment 
of the under cells of the frond with the exception of the peripheral ones. The 
figures of Batrers and HEYDRICH show a great number of large hyaline cells in 
the interior of the frond, suggesting that the erect cell-rows from which they arose 
consisted of about 10 cells. Such figures represent, according to my observations, 
eccentric sections in which a greater 
number of the outward bent cell- 
rows have been intersected. Accor- 
ding to Kyrın, the cells of the basal 
layer remain for a long time un- 
changed, and differ from the cells 
of the inner tissue through their 
small sizeand rich contents. ”Schliess- 
lich tritt indessen auch eine Ver- 
grösserung in den Zellen der Basal- 
scheibe ein, indem sie sich zwischen 
die vergrösserten Basalzellen der 
verticalen Zellfäden einkeilen.‘“ This 
latter assertion is not in accordance 
with my observations. In specimens 
attaining only a smaller height, being 
i Fig. 119. only cushion-shaped, the cells of the 
ana Geo basal layer seen trom below, bovin basal layer remain often unchanged, 
vertical section, showing a young hair. C, vertical section of but in typical specimens of the in- 
disc-shaped frond showing a sorus sunk in a groove. 350:1. 
flated form they are enlarged at an 
early period, and there seems to be ordinarily no question of protruding of these 
cells between those of the second layer. But the cells increasing not only in length 
but also in breadth, there is no room for all the cells of the basal layer when 
enlarging their volume, and a number of them must therefore remain unchanged 
in size. Connected with the growth of the inner cells is the enlargment of the surface 
of the frond which makes its appearance in the lateral branching of the cell-rows 
in the periphery of the frond (fig. 120 C). — In the large vesicular cells a number 
of small chromatophores are easily visible; in some cases these cells were poor in 
cell-contents, in others they contained small starch grains. 
The simultaneous occurrence of the two forms of the species on the same 
leaf of Zostera is very curious. As a rule, the specimens growing on the faces of 
the leaves are disc-shaped or low cushion-shaped, while those placed on the margins 
are inflated. Cushion-shaped specimens may, however, be found on the margins 
and inflated on the faces, thus the two forms of specimens may occur side by side 
MAN 
ST 
apparently under equal external conditions; this may perhaps be caused by a different … | 
