short distances asunder (revealing the joints of the internal axis), and the 
whole surface is reticulated with anastomosing cells. Fructification: 1, 
Ceramidia, densely crowded on the ramuli, ovate, sessile; rarely produced : 
2, tetraspores imbedded in the multifid, lateral ramuli. Substance cartila- 
ginous and firm, the tips of the branches standing out, and each retaining 
a drop of water when the specimen is lifted into air. Colowr a dark purple, 
changing into olive green, and finally to amber-yellow under the influence 
of sunlight. 
ee een 
I have always thought that in whatever genus we put Ryfi- 
pllea complanata of Agardh, in the same we must place not only 
the Polysiphonia thuyoides of British authors, but P. fruticulosa 
also. ‘The internal structure of these plants is identical. They 
all possess a central jointed axis composed of many tubes, like 
the frond of Polysiphonia, coated on the outside by a broad band 
of small irregular cells. The surface appears reticulated under 
the microscope, and marked at short intervals by dark-coloured 
transverse lmes. These characters belong to the frond of Ryt- 
phlea, m which genus Agardh places the first of the three plants 
in question ; while both the latter have hitherto been referred to 
Polysiphonia. As I have already (PI. CLXX.) adopted Agardh’s 
name for the former, I am now constrained to alter the posi- 
tion of the two latter, and transfer them from Polysiphonia to 
Rytiphlea. These three plants have not only a similar structure, 
but have so much the same natural habit, that specimens may be 
found which bring them zzconveniently near each other. Some 
specimens of FR. fruticulosa are very close to some of &. thuyoides, 
and the latter, in like manner, closely approaches narrow states 
of R. complanatu. So nearly do they approach, that at one time 
I regarded them all as merely sportive forms of one species, but 
this was before I had much opportunity of studying them in a 
living state. When growing, each possesses characters  sutffi- 
ciently obvious. It is only in a few cases of imperfect or badly 
dried specimens that the student will find it difficult to decide 
to which species the specimen should be referred. 
The ceramidia of this species are not often found, but when 
they occur they are generally formed in profusion, almost every 
twig bearmg one or two. ‘They are always borne on less luxuriant 
specimens than those which yield tetraspores. 
Fig. 1. RyrreHL®a FRUTICULOSA :—of the natural size. 2. Small branch with 
~ ceramidia. 3. A ceramidium in sifu. 4. Small branch from another plant. 
5. Ramulus with imbedded ¢etraspores. 6. Tetraspore. 17. Portion of the 
stem. Section of the same :—all more or less magnified. 
