SEA WEEDS 375 



includes a common species (0. dasyphylla), with thick fronds, that 

 is found in shallow sandy pools, where it grows on pebbles, shells, 

 or on other weeds, the colour varying from pink to a dark purple. 

 C. tenuissima is a very similar weed, but may be distinguished by 

 its more slender growth, and by its long, rod-like simple branches, 

 clothed with slender, bristle-like branchlets that taper from the 

 middle towards both ends. 



On the northern coasts of Britain we may meet with Odonthalia 

 dentata, the blood-red fronds of which are tufted, and arise from a 

 hard, disc-like root. Each frond projects from the axil of a tooth- 

 like projection of the main stem, and is deeply pinnatifid, with a 

 distinct midrib in the lower part, and thin and membi-anaceous 

 towards the tip. The puma are dentate, and the spores are in 

 stalked, oval conceptacles in the axils of the pinnae. The tetra- 

 spores are similarly situated in stalked, lanceolate leaflets. 



The weeds of the genus Rytiphlcza are very similar to some of 

 the Polysiphonia, the axis of the frond being jointed and trans- 

 versely striped, but the nodes are less distinct and are not 

 constricted. They are shrub-like weeds, with tufted spores in oval, 

 sessile conceptacles ; and tetraspores in spindle-shaped branchlets 

 or in little pod-like leaflets. The principal British species 

 are: 



2?. pinastroides, a much-branched and shrub-like weed, of a 

 dull-red colour, which turns black when the plant is dried. The 

 branches have rigid, hooked branchlets arranged in such a manner 

 as to give a combed appearance. This species occurs on the south 

 coast, and is in its prime in very early spring. It is often rendered 

 peculiarly interesting by the colonies of zoophytes and the patches 

 of Melobesia with which it is more or less covered. 



.R. fruticulosa is another shrubby species, with irregularly 

 branched, interlacing stems. It is to be found in the rock pools 

 of the south and west coasts, and is of a deep-purple colour in 

 the deeper shady pools, but varying to a yellowish tint where 

 exposed to the full light of the sun. The whole of the frond is 

 covered with hooked branchlets, and the weed is peculiar for the 

 fact that, when removed from the rock pool, little glistening beads 

 of water remain attached to the tips of the terminal branches. The 

 tetraspores are situated in distorted branchlets. 



B. thuyoides has creeping, fibrous roots, from which arise the 

 erect stems of purple-brown, branched fronds with short spine-like 

 branchlets. It occurs in the shallower rock pools, where it grows 



