On THE PITHOPHORACEA. 9 
slightly in Pithophoracew. The narrowest cells I have seen (belonging to 
the branches in P. kewensis nob.) have had a diameter of 40 ua, 
and the thickest (belonging to the principal filament in P. Roettlert nob.) 
a diameter of 190 w. The length varies more, however. Generally they 
are rather long, 5—20 times as long as thick, but cells that are not 
much more long than thick are also found, as well as those that are, 
on the contrary, more than 100 times as long as thick. 
As to their position in the thallus, the vegetative cells may be 
divided into two kinds: the inclosed and the terminal. The inclosed 
cells are those that are placed in the series of cells, and thus are in- 
closed between two other cells. Terminal are those that end a series 
of cells, and thus touch another cell with only one end. The inclosed 
cells are most frequently almost purely cylindrical with abrupt ends. The 
small deviation from the cylindrical form, which the cells in some species 
show, consists in the cells having their longitudinal walls very slightly 
convex (pl. 1, fig. 6, 7). Of the inclosed vegetative cells two kinds are 
easily distinguished, viz. those of a green colour and those which are 
not green. The green-coloured, which are the cells that prepare the 
food of the plant, have received their colour from pure chlorophyll. 
Those parts of the parietal protoplasm which are coloured by this sub- 
stance (the so-called granules of chlorophyll) have, in general, a lens- 
formed shape, with the line of circumference generally broken in obtuse 
angles (pl. 3, fig. 1). In specimens gathered in the afternoon, when the 
sun has influenced them for a sufficiently long time, a small granule of 
starch may be very clearly distiguished in each granule of chlorophyll 
(pl. 3, fig. 1, 3). The granules of chlorophyll are, as a rule, arranged in 
one layer, which is seldom uninterrupted, but usually has greater or 
smaller openings. Not rarely these openings are so great, that the arrange- 
ment of the granules of chlorophyll looks like a net, as pl. 3, fig. 3 shows. 
In sterile specimens the cells now described are the only existing 
ones, but in fertile specimens colourless cells are found besides the 
green ones. The colourless cells, which are the subsporal branchless 
cells before mentioned, differ from the coloured ones by having their 
layer of parietal protoplasm much thinner, and by an almost total want 
of granules of chlorophyll. (On the cause of this, see the paragraph 
on »The reproductive orgaus.») A few such granules are, however, 
usually left, especially in the upper part of the cell, situated nearest to 
the (sister-) spore, (pl. 3, fig. 7; pl. 4, fig. 3, 9,.16 and others); but 
they are not sufficiently numerous to give the cell a green colour. 
Nova Acta Reg. Soc. Ups. Ser. III. 2 
