86 COMMON SEAWEEDS. 



remembers that on our coarser weeds not fit for the 

 album we find our greatest treasures. The filaments 

 of this Callithamnion are fine as cobwebs, often laden 

 with fruit, and it is a beautiful object when mounted 

 for the microscope as I have directed in the chapter 

 on mounting seaweeds. The stem consists of simple 

 joints, without veins. The favell<s are large double 

 berries, transparent, full of spores. The tetraspores 

 large and not crowded on the pinnules, rarely more 

 than two on each, which enables us to see them better. 

 The tips of the branches are tufted with colourless, 

 exceedingly fine filaments. Quite a native of Britain; 

 not noticed elsewhere. 



. Callithamnion Polyspermia. — A very common 

 species. It grows upon other plants : Fucus Vesicu- 

 losus and Fucus Serratus. Sometimes quite chokes a 

 young frond with matted fibres of brownish red or 

 pale purple. It is not large : the tufts are but from 

 one to three inches in diameter ; but they are so pro- 

 lific that the little forest soon overruns its ground. 

 It is worth examining, for the transparent stem shows 

 well the narrow cell of rosy hue within, and on the 

 branches sit close rows of tetraspores or a heavy 

 cluster of berries (favellce), or a third kind of fruc- 

 tification — those little-known antheridia — a kind of 

 vivaparous tetraspore, says Harvey. Any way, these 

 mysterious dots are in a chapter of Grod's works not 

 yet spelt out. 



Callithamnion Spongiosum. — Dark-coloured, 

 closely matted, and not very interesting. Pound 



