184 BRITISH SEA-WEEDS. 



spherical conceptacles, which protrude from the branches 

 and branchlets. 



This plant grows on rocks near low-water mark, and 

 is annual. It occurs most frequently on the south and 

 west of England, and on the shores of Ireland and the 

 Channel Islands. It is considered rare, but this may 

 probably be partly due to the fact that it matures in 

 winter, when it is very likely to be overlooked. Perhaps 

 the best way to make out the genus is to examine a thin, 

 vertical section of a frond under a microscope, which 

 will reveal the peculiar arrangement of netted longitu- 

 dinal fibres in the centre, and the closely-packed, ver- 

 tical filaments which form the bark. The specific dis- 

 tinction is less difficult to establish, as the general habit 

 of the plant is very different from that of either of the 

 other British species. 



Gigartina pistillata. The pedicellate Gigartina. 



Root a broad disc, without fibres ; frond two to six inches 

 high, flattened, destitute of branches below, branched in a 

 fan-like manner above ; branches repeatedly forked, spread- 

 ing, with rounded axils and acute tips. Spores in globular 

 conceptacles, which are produced abundantly on the branches, 

 either singly or two or more together ; tetraspores cruciate, 

 immersed in clusters in the substance of the brandies. 



This species is even more rare than the last ; it ap- 

 pears to be most abundant on the coasts of Cornwall 

 and Devon. The mode of branching, and the form and 

 greater number of the conceptacles are very obvious and 

 well-defined characters. This plant grows on rocks, near 

 low-water mark, in winter, and is nerennial. 



