465 
which only appear in the second or third and following joints. In P. Brodiawi and 
P. nigrescens, which have 7—8 and 12—17 pericentral cells respectively, the next 
following one to four joints had 4 pericentral cells (figs. 384, 396), an interesting 
fact when we remember that a great number of the species of this genus have con- 
stantly 4 pericentral cells. The normal number of pericentral cells in the said 
species is gradually reached in the following joints. 
8. Secondary pits are produced not only between pericentral cells but also 
between the cortical cells and between these and the pericentral cells (Pol. violacea, 
P. Brodiwi). Cells connected with more than one secondary pit in the same wall 
occur in Pol. elongata, Rhodomela and Odonthalia. In Pol. elongata the pericentral 
cells are first connected by one secondary pit, but later on, in the following year, a 
circle of further secondary pits arises in the same wall (fig. 357). 
9. The tetrasporangia arise in a pericentral cell. According to FALKENBERG (1901 
p. 88) they always originate in the Polysiphoniæ from the oldest pericentral cell in 
the segment. This is, howewer, not in accordance with my observations. As early 
as in 1884 I have ascertained that the sporangia in P. fastigiata take their rise in 
a lateral pericentral cell separated from the oldest one by two or three sterile peri- 
central cells (1884 p. 10, rés. p. 2, figs. 1—3). In P. violacea and LP. Brodiei I found 
that the first pericentral cell is cut off to the right of the trichoblast, while the 
fertile pericentral cell is always situated to the left of the trichoblast borne on the 
same joint, and is probably the second pericentral cell. The fertile cell cuts off two 
secondary pericentral cells, and the inner cell is then divided by a horizontal wall 
into a stalk cell and a spore-mother-cell or tetrasporangium. In the species of Poly- 
siphonia with 4 pericentral cells a small peripheric cell is further cut off under 
one of the secondary pericentral cells which is a little shorter than the other, and 
this little cell is always situated beside the basal cell of the trichoblast of the fore- 
going joint, on its right side. This cell is always present in P. violacea and P. or- 
thocarpa. In P. urceolata and P. elongata it may be present or wanting; in the first 
named species it was present in the trichoblast-bearing stems, while it was wanting 
in the stems without trichoblasts. It is further usually present in P. Brodiei which 
has 7—8 pericentral cells, but it is wanting in P. atrorubescens and P. nigrescens where 
the number of pericentral cells is greater. In the species with 4 pericentral cells in 
the sterile joints the number of pericentral cells in the fertile joints is always 6, 
though there are always only two secondary pericentral cells. 
Fam. 14. Delesseriaceæ. 
J. G. AGARDH, 1852, Species genera et ordines Algarum. Vol. II pars 2. Lunde. 
— , 1898, — Vol. III pars 3. 
R. Korkwırz, (1900), Beiträge zur Biologie der Florideen. Wissensch. Meeresuntersuch. Neue Folge. IV. 
Band. Abt. Helgoland Heft 1. Kiel und Leipzig. 
