RHODOSPERME A. 107 
is, doubtless, due to the large number of siphons, which is generally 
twenty, and these being set so closely together, very naturally account 
Fic. 100. Magnified branchlets of Rytiphlea fruticulosa. (a) Capsules. 
(b) Tetraspores in the swollen ramuli. 
for the dark tint of this species. A transverse section of the stem is 
seen at a, Fig.101. P. affinis, usually regarded as a rarity, is a variety of 
P. nigrescens. The stem contains about sixteen siphons. The ceramidia, 
Fie. 101. (a) Transverse section of Polysiphonia nigrescens ; (b) Ditto of P. fastigiata; 
(c) Ditto of Polysiphonia fibrata; (ad) Ditto of Polysiphonia parasitica; (e) Ditto 
of Polysiphonia variegata. 
or spore-vessels of P. nigrescens are ovate and sessile, or produced from 
the sides of the branches, but in P. affinis, they are nearly round, and 
ie 
