SEA WEEDS 853 



resembles another species (C. arcta), which grows in dense tufts on 

 rocks, but the latter is larger, not so slender, and more freely 

 branched. The cells, too, of C. arcta are longer, being about ten 

 times the length of the diameter, and the fronds are silvery at 

 the tips. 



Nearly thirty species of Cladophora have been described, but it 

 is impossible to give here a detailed description of all. We add, 

 however, a brief summary of the distinguishing features of a few 

 other species that are common on our coasts. 



C. rupestris is common everywhere, and easily recognised by its 

 rigid, branching, tufted fronds, of a dark greyish-green colour ; its 

 branches, which are opposite, bear awl-shaped branchlets. It is 

 found in rock pools from half -tide downwards, and in deep water 

 beyond the tide-marks, the plants growing in the latter situa- 

 tions being generally of a fine dark-green colour. 



C. Icetevirens is also very common on rocks between the tide- 

 marks. Its fronds are tufted and freely branched, of a pale-green 

 colour and soft flexible texture, and about six inches long. The 

 branchlets are usually slightly curved. 



C. gracilis is a beautiful plant that grows on large weeds, 

 especially the Sea Grass (Zostera) in deep water ; and although not 

 very common, it is sometimes found on the beach after storms. It 

 is characterised by its slender silky fronds, from a few inches to 

 a foot in length, of a yellowish -green colour. It may always he 

 known by the comb -like branchlets growing only on one side of 

 each branch. 



C. refracta grows in dense tufts, two or three inches long, in 

 rock pools near low-water mark. Its fronds consist of rigid stems 

 in rope-like bundles that are very freely branched, the whole tuft 

 being of a yellow-green colour and silky texture. C. albida closely 

 resembles it in structure and habit, but may be distinguished by its 

 paler colour, which disappears when the weed is dried, and by its 

 longer and more delicate branches. 



In another order of the green-spored algae (the Siphonece or 

 Siphonacece) the frond is formed of single branching cells, and 

 many of these are often interwoven into a spongy mass, and some- 

 times coated with a deposit of calcareous matter. 



In the genus Codium the fronds are of a sponge-like texture, 

 composed of interwoven branching fibres, and are of a globular, 

 cylindrical, or flattened form. The commonest species is C. tomen- 

 tosum (Plate VII.) > which consists of sponge-like, dark-green 



