358 THE SEA SHORE 



the female cells are generally produced on different plants of the 

 same species. 



We will now proceed to examine some of the best known and 

 most interesting of the rhodosperms, beginning with the order 

 Ceramiacece, which contains a number of red or reddish-brown 

 weeds with jointed, thread-like fronds that enclose a single tube, 

 and which are generally surrounded by a cuticle of polygonal cells- 

 The spores are contained in transparent berry-like sacs which are 

 naked ; and the four-parted spores (tetraspores) are formed in the 

 cells of the cuticle or at the tips of the fronds. 



Over twenty British species belong to the genus Callithamnion, 

 and nearly all of them are pretty red or rose-coloured, feathery 

 plants that are conspicuous for their beauty. Nearly all are of 

 small size, the largest measuring only seven or eight inches, while 

 some are so small that they would scarcely be noticed except by 

 those who search diligently for them. The principal features of 

 the genus are, in addition to those mentioned above as common 

 to the order, that the spores are angular, and clustered within a 

 transparent sac, and the tetraspores are naked and distributed on 

 the branches. 



In some species the fronds have no stem, and these are very 

 small, generally only about a quarter of an inch in height or less, and 

 they grow on rocks or weeds, sometimes clothing the surfaces with 

 a velvet-like covering. C.floridulum forms a kind of reddish down 

 on the rocks, sometimes in little rounded patches, but sometimes 

 completely covering the surface. It occurs on several parts of the 

 English coast, but is so abundant on the west coast of Ireland that 

 the beach is strewn with it after stormy weather. Other allied 

 species grow in minute tufts on rocks, or are parasitic on other 

 weeds, and are so inconspicuous that they are but little known. 



Another section of the genus is characterised by pinnate fronds 

 with opposite segments, and the species are very pretty plants with 

 fronds generally a few inches in length. One of the commonest of 

 these is the Feathered Callithamnion (C. plumula), a great favourite 

 with collectors of sea weeds, and a most interesting object for the 

 microscope. Its soft and flexible fronds grow in tufts from two to 

 five inches long. The branches are regularly arranged, and the comb- 

 like branchlets bear the tetraspores on the tips of the plumules. 

 This beautiful weed grows near low-water mark, and in deep water, 

 and is often very abundant on the beach after storms. C. Turneri 

 is another common species, easily known by its creeping fibres, 



