has hitherto been regarded as a distinct species though in its morphology il exactly 
agrees with P. violacea and only differs by very variable characters such as those men- 
tioned. Harvey indeed observes of P. fibrillosa (Phye. Brit. Pl. 302, 1851): “It is most 
nearly related to P. violacea, with which alone can it well be confounded, and from 
which it chiefly differs in its shorter and less multified ramuli, duller colour, and 
shorter articulations; but there are specimens occasionally found which seem almost 
to connect these two species together”. J. AGARDH, REINKE and Kyrın admit too the 
relation of the two species but nevertheless consider them as distinct. After having 
examined a great number of spec- 
imens from numerous localities in 
the Danish waters I have arrived 
at the apprehension that it is im- 
possible to draw a natural line of 
demarkation between them. In too 
many cases it depends on an arbi- 
trary estimate whether a specimen 
may be referred to the one or the 
other of the two species, and I 
have therefore arrived at the con- 
clusion that LP. fibrillosa must be mic CFA 
regarded as a form of P. violacea Polysiphonia violacea. Division of tetrasporiferous joints. b, basal 
distinguished principally by shorter el! of trichoblast; p, small peripheral cell; s, stalk cell of spor- 
aS 2 4 angium; X small cell establishing the secondary pit between the 
joints and stronger cortication. The pericentral cells. 636 : 1. 
trichoblasts are strongly developed 
and much branched, at the base up to 28 « thick. The straw-colour of the frond 
emphasised by REINKE is entirely due to an intense light. It grows only in slight 
depths and in rather light places, and usually also in more agitated water, and 
these conditions undoubtedly produce the characters mentioned. 
In f. fibrillosa the joints in the upper part of the frond are about 11/2 (1—2) 
times as long as the diameter. In f. fypica they are longer, usually 3—5 times as 
long as broad. In this form the main axis is distinct as is the case also with f. 
fibrillosa. But the thickness of this axis is variable, and in the finer forms it is 
scarcely thicker than the principal branches. In f. fenuis the principal axis is thin 
and not discernible from the branches; the joints are longer, c. 6—9 times as long 
as broad, the cortication almost wanting, the secondary axillary shoots are scarce, 
and the trichoblasts simple or feebly branched, often with rose-coloured chrom- 
atophores. This form grows in localities with feebler light and less agitated water, 
principally in fjords and in great depths. 
F. aculeata is a loose sterile form characteristic by its squarrose branches and 
by wanting cortication. It has usually numerous secondary axillary branches which 
in spreading at tight angles give to the plant a characteristic appearance (fig. 374). 
Sometimes, however, the secondary branches occur only rather sparsely, and the 
