On the Pithophorace^. 9 



slightly in Pithophoraceœ. The narrowest cells I have seen (belonging to 

 the branches in P. keicensis nob.) have had a diameter of 40 ;(, 

 and the thickest (belonging to the principal filament in P. Roettleri noh.) 

 a diameter of 190 />. 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 arc also foiuid, as well as those that are, 

 on the contraxy, 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 ^\^th 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 (pi. 1, fig. 6, 7). Of the inclosed vegetative cells two kinds are 

 easil}- 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 Avhich 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 (pi. 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 

 (pi. 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 pi. 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, difier 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 organs.») A few such granules are, however, 

 usually left, especially in the upper part of the ceil, situated nearest to 

 the (sister-) spore, (pi. 3, fig. 7; pi. 4, fig. 3, 9, 16 and others); but 

 they are not sufficiently numerous to give the cell a green colour. 



Nova Acta Rog. Soc. Ups. Sor. III. 2 



