THE GENUS POLYSIPHONIA. 273 
Hutchinsia. This, however, was objected to by Greville (Fl. Edinensis, 
1824, p. 308) owing to the possibilities of confusion with Grammitis which 
had already been used for a group of Fungi, and by Swartz in 1801 for a 
genus of Ferns, which was a synonym for Polypodium. Greville therefore 
devised the term Polysiphonia, which has persisted in spite of the indignation 
of Desmaziéres (21), who was reluctant to abandon the term which had the 
privilege of seniority, for one “ qui parait devoir son existence au caprice.” 
MORPHOLOGY. 
The Polysiphonia plant consists of a branched thallus, bearing numerous 
ramuli. In perennial forms like P. elongata the ramuli are shed annually 
before the winter, the plant being re-clothed in the spring. At the tips of 
the branches and of the ramuli, clusters of fine filamentous hairs are borne 
in many species, and on these the antheridia are produced. Tetraspores are 
borne in the ramali, and cystocarps may be developed either on the ramuli 
or on the branches of the thallus. The attachment of the plant is effected 
by the development of numerous rhizoids. 
ANATOMY. 
The species are divisible into two main groups :— 
(a) Ecorticate, 
(6) Corticate. 
The anatomy of the ecorticate forms consists solely of siphons, that is of cells 
which extend the whole length of the articulation (Pl. 22. fig. 5). In the 
corticate forms, however, in addition to the siphons, there are cells present at 
the periphery of the thallus which are much shorter than the siphons and 
gmaller in diameter. These form a mosaic which may extend over the whole 
plant as in P. fruticulosa, or may only occur on the lower parts as in 
P. violacea (Pls. 25, 24. figs. 78, 59). 
The thallus consists throughout the group of one central siphon and a 
band of primary pericentral siphons numbering from 4 to 20 or even more. 
These may be surrounded by alternating bands of smaller siphons, and 
bounded externally by one or more rows of cells, in the corticate forms. 
The pericentral siphons are usually parallel to the main axis. In P. atro- 
rubescens, P. nigrescens var. e. affinis, and occasionally in P. fibrata, however, 
a slight spiral formation is visible, and the same phenomenon is well defined 
in what is believed to be a new species, and has been here described as 
P. spiralis. 
P. urceolata will serve to typify the ecorticate species. The thallus con- 
sists here of one central siphon, and four pericentral in each articulation. 
'The central siphon is much smaller than the pericentral ones, and there is 
protoplasmie continuity throughout the plant. The upper and lower ends of 
the siphons are connected by almost colourless strands of protoplasm, which 
LINN. JOURN.--BOTANY, VOL. XLVI. X 
