202 MR. R. J. HARVEY GIBSON ON THE 
(* Phycologia Britannica,’ pl. cxx. B.) in the following words :— 
“Spreading over the surface of rocks, about half-tide level.” 
Conferva purpurea, Dillw., which Harvey unites with R. Rothit 
under the name of Callithamnion Rothii, he describes as being 
found * on maritime rocks, within the influence of the spray, but 
beyond the reach of ordinary tides.” I have collected specimens 
of Rhodochorton Rothii at all levels from extreme low water at 
a 20-foot tide to two or three feet above high-water mark, and 
found that the nearer the plant grows to low-water mark the 
larger, brighter, and more branched it becomes. 
General accounts of this species are given by Kützing *, J. G. 
Agardh T, Hauck f, and Thuret $. 
Rhodochorton Rothii occurs in the form of broad velvet-like 
expansions of a dull erimson colour, from 2 millim. to 1 centim. 
in thickness. The upright filaments arise from a densely inter- 
woven ereeping network of filaments, the cells of which are about 
as long as broad. The erect filaments are of uniform diameter 
throughout, the cells being about one and a half to two and a 
half times as long as they are broad. The branches arise alter- 
nately and at very acute angles with the main axis. The branching 
is very sparing, save near the apex. 
The dense corymbose clusters of sporangia (tetrasporangia) 
are terminal or subterminal, and their position and mode of 
origin furnish a good diagnostic difference between this species 
and R. fforidulum, Näg., and R. chantransioides, Reinke, where 
they arise secundly along the branches. 
Their mode of development is as follows :—Copious terminal 
branching first of all takes place in the apical region of a vegetative 
filament, the secondary branches arising as buds from the 
penultimate cells of the primary branch. The sporangia arise 
usually on branches of the fourth order, Each sporangium is 
formed from a bud of the penultimate cell of a branch, the bud 
becoming separated from the parent cell by an oblique septum 
(Pl. XXXIV. fig. 11). The cell then loses its oblong cylindrical 
shape and becomes oval, the narrower end being next the parent 
cell. The contents segment transversely to the long axis, the 
two halves again dividing parallel with the long axis. The spores 
* * Species Algarum,’ p. 640. 
t ‘Species, Genera, et Ordines Algarum, ii. PG uL p l3: 
t ' Die Meeresalgen Deutschlands und Oesterreichs,’ p. 68. 
$ In Le Jolis' ‘ Liste des Algues marines des Cherbourg,’ p. 111. 
