444 
The species is very common in all the Danish waters. It is perennial and may 
be found in well developed and large specimens in all the seasons. In winter there 
Fig. 400. 
Polysiphonia nigrescens. Ripe cystocarp. 130 : 1. 
is no or almost no growth, and the wintering 
shoots have no trichoblasts. In spring the 
plants are in full vegetative development 
with numerous hairs, and sexual organs 
occur. Thus antheridia and carpogonia were 
met with in April to June. Ripe cystocarps 
were met with in (May) June to September. 
Young tetrasporangia were found in April 
and May, ripe in May to September. The 
fructiferous branches seem to be thrown off 
in August and September, for in the follow- 
ing months the species was always found 
sterile. The denudate plants may produce 
new shoots in the following year as well as 
the young plants produced by the germinat- 
ing spores in summer. The plants arising from 
early germinating spores may without doubt 
produce ripe spores in the same season while those germinating in the later part 
of the summer probably pass the winter in a sterile state. The denudate specimens 
bearing short remnants of the fruc- 
tiferous shoots, may be referable to 
f. senticosa. Most of the specimens may 
be referred to f. fucoides. F. pectinata 
was met with in exposed localities in 
the North Sea and the Skagerak. In 
deeper localities in the inner waters 
slender specimens occur which may in 
part be referred to f. flaccida Aresch.! 
Other specimens from deeper localities 
were slightly branched and ought there- 
fore to be referred to f. reducta Svedelius, 
described from the inner Baltic Sea. 
— The species thrives best in depths 
smaller than 15 meters, where it is 
very common, even in very light local- 
ities. Under that level it occurs rather 
rarely and only in small quantities. 
1 When ÅRESCHOUG (1. c. p. 49) says that 
the branches änd branchlets in this form are 
subhorizontal, it does not seem to be justified. 
Fig. 401. 
Polysiphonia nigrescens. A, portion of tetrasporiferous branch ; 
b, basal cell of trichoblast; c, central cell; s, stalk cell; sp, 
sporangium. B, similar in longitudinal section. C, D, trans- 
verse sections of sterile joints, E, F, of fertile joints of 
tetrasporiferous branches. A 95:1. B—F 200: 1. 
