106 BRITISH MARINE ALG. 
and, under the influence of sunlight, becoming an amber yellow or pale 
straw colour. The fronds are sometimes from 6in. to 10in. high, very much 
branched, and set with numerous more or less tufted multifid ramuli. 
These ramuli are frequently tipped with antheridia, which are often pro- 
duced so abundantly as to impart a prevailing yellow tint to the whole 
plant. Both forms of fructification are very well represented at Fig. 100: 
a isa branchlet, producing several little capsules, seated here and there 
on the sides of the twig-like branches ; } is a branched ramulus containing 
tetraspores in the swollen or distorted articulations. 
The beautiful and extensive genus Polysiphonia is represented by some 
of its species in all seas, from the poles to the equator. According to 
some writers there are upwards of 200 species of these plants known 
to botanists, some five or six-and-twenty of which are found on various 
parts of the British coasts. They vary greatly in size, in habit, and in 
colour; some being nearly 2ft. in length, and others barely 2in. high. 
Several species, when fully grown, are robust, bushy, and tree-like, while 
others are of extreme delicacy, the branches being finer than the finest 
human hair, resembling the most delicate exotic ferns in miniature. In 
colour they vary from a brilliant crimson to different shades of brown, red, 
and purple, and occasionally even approach a blackish tint. The structure 
of their stems and branches is well expressed in the generic name, which 
signifies ‘‘ many siphons,” the stems of all containing four or more primary 
cells or siphons, those of simple structure having four primaries in each 
articulation or joint, while others have as many as twenty four. These 
siphons are arranged round a central cavity, exactly like the spokes of a 
wheel around the axle-tree, and the regularity with which these siphons 
occur as regards number, is generally, in the absence of fruit, a pretty 
sure guide for the identification of species. A transverse cutting of the 
stem of a Polysiphonia fresh from the sea, placed under the microscope, 
or upon aslip of glass, and held under a lens, will reveal the beautiful 
structure of these plants most satisfactorily. When viewed thus, the 
central tube of some species will be found to be empty, while in others 
it is filled with endochrome like that of the siphons around it; and in those 
species of a more complicated structure, the main stems are seen to be 
coated externally, with more or less numerous small cells, in addition to 
their primaries. All these characters are very well represented in Fig. 101. 
The following are those species which are most commonly met with on 
the British shores. Fig. 102 represents some branches of the well-known 
Polysiphonia nigrescens, which is a very common plant found in rock pools 
in every situation where seaweeds grow, and, being perennial, is met 
with in all seasons; but the only specimens which are sufficiently at- 
tractive to the collector are those which are found in the spring, when 
the branches throw out their pretty tufts of fine red filaments. The 
nearer to low-water mark such specimens are taken the better, otherwise 
the stems and lower branches of this species, when dried, become perfectly 
black and opaque. The dark colour, or opacity, in the stems of this species 
