200 
PACIFIC SCIENCE, Vol. XXII, April 1968 
Fig. 4. Polysiphonia dotyi, photomicrograph of 
a vegetative branch apex. 
4-6 unequal dichotomies, soon deciduous leav- 
ing small scar-cells in both prostrate and erect 
branches; tetrasporangia to lOOp in diameter, 
in spiral sequence near branch apices, consider- 
ably distending the segments at maturity; sper- 
matangial branches 140-200 X 60-7 5 p, oblong 
with broadly rounded tips, arising as a primary 
branch of a trichoblast. 
Plantae praecipue prostratae aut interdum scan- 
dentes; rami prostrati erectique plerumque 140-I60p. 
diam.; rhizoidea unicellularia, plerumque discoidea, 
interdum multi cellularia; connectionem latam apertam- 
que cum cellulis pericentralibus habentia; rami erecti 
non numerosi, 0.5-1 .0-( 10 ) mm alt., segmentis pler- 
umque brevioribus quam lata, necnon tumidis, prae- 
cipue supra; rami laterales pauci, in associatione cum 
trichoblastis enascentes; cellulae peri centrales plerum- 
que 8-10, ecorticatae, in segmentis successive ex ordine 
sitae; trichoblastae una in unoquoque segmento, per 
unam cellulam pericentralem inter trichoblastas suc- 
cessivas spiraliter versae; maxima ex parte elemen- 
tariae, interdum, autem, ad 1.2 mm long., et 4-5 
dichotomias inaequales habentes, mox deciduae, cellu- 
las-cicatrices parvas in ramis et prostratis et erectis 
relinquentes; tetrasporangia ad 100(X diam., in spira 
prope apices ramorum, dum maturuent segmenta 
aliquantum distendentes; rami spermatangiales 140- 
200 X 60-75P-, oblongi, in cacuminibus late rotundati, 
ut ramus primarius trichoblastae enascentes. 
type: H. 48-1213.16, tetrasporic, Amen L, 
Bikini Atoll, July 7, 1948. 
ADDITIONAL COLLECTIONS: PHOENIX ISLANDS 
— L. 2433.2, spermatangial, on Halimeda sp., 
McKean I., Oct. 19, 1964; marshall islands 
Fig. 5. Polysiphonia dotyi, photomicrograph of a 
branch apex bearing spermatangial stichidia. 
— D. 9693A, on reef drop-off, lagoon side near 
Ine Village, Arno Atoll, legit Leonard Horwitz, 
Aug. 22, 1951; H. 48-0914.25, outer reef, Uku 
L, Bikini Atoll, July 9, 1948; H. 48-1091.15, 
on Pocockiella, outer reef Arji L, Bikini Atoll, 
July 12, 1948; H. 48-2894.6, tetrasporic, on 
Udotea sp., Nama I., Bikini Atoll, July 15, 
1948; CAROLINE ISLANDS — D. 23688.2, on dead 
coral on reef at Quoi L, Truk Group, legit E. 
Menez, Aug. 2, I960. 
An unusual feature of this species is the 
broad open connection of the rhizoids with the 
pericentral cells. The writer is not aware of this 
feature occurring in any other species with more 
than 4 pericentral cells. A feature which it 
shares with only a few species, including P. 
howei, is the offset position of the pericentral 
cells. 
Polysiphonia exilis Harvey, 1853:47 
Figs. 1 C, 3 C 
Plants epiphytic or on dead coral, chiefly 
prostrate, attached by unicellular rhizoids, com- 
monly with digitate or bulbous tips, cut off by 
a cross-wall from the center or proximal end 
of the pericentral cells, mostly short but oc- 
casionally as much as 2 mm long; pericentral 
cells mostly 9-11, around a relatively large 
central cell, ecorticate, in straight rows longi- 
tudinally; walls to 20[i thick, often stratified; 
erect branches 3-6 mm high and 160-17 Op in 
diameter, with segments mostly 0.5-0.75 diam- 
eters long, arising almost exclusively cicatrigen- 
ously from the prostrate branches and having 
few or no lateral ramuli; trichoblasts on erect 
