Poly sip honia in Hawaii — Menez 
209 
of all the Polysiphonia species described in this 
paper are exogenous. 
Hollenberg (1942) described two types of 
exogenous branches: (1) normally exogenous 
branches, arising directly from the branch pri- 
mordia, and (2) cicatrigenous branches, devel- 
oping from the scar cells after the trichoblast 
has fallen off. 
C. Antheridia 
The antheridia usually occur as primary 
branches of the trichoblasts or may occur on the 
trichoblasts, covering the lower part of the latter. 
At the apex of each antheridium a sterile tip of 
one or more cells may be found. Each antherid- 
ium is usually supported at the base by a two- 
celled stalk. 
D. Cystocarps 
Poly sip honia cystocarps are very variable in 
shape. They are usually urceolate, ovate, or 
oblong and seem to be little used for systematic 
or taxonomic purposes. 
E. Rhizoids 
The rhizoids occur at the base of the thallus. 
While they may also be found on the axis above 
the thallus base they are never found near the 
thallus apex. The rhizoids may occur singly or 
several may be produced from a segment of the 
thallus. They arise as outgrowths from the proxi- 
mal end or middle of the pericentral cells. They 
are commonly unicellular, but sometimes multi- 
cellular. Each may or may not be cut off by a 
cross-wall at Its proximal end from the support- 
ing pericentral cell. The tip of the rhizoid may 
be simple, digitate, or discoid. 
F. Pericentral Cells and Cortical Cells 
In the tetrasiphonous species of Polysiphonia 
( Segi, 1951), the number of pericentral cells 
is usually constant throughout the entire thallus, 
while in species with more than four siphons 
the number of pericentral cells may vary in the 
different parts of the thallus. 
Cortical cells may be observed in some species. 
They are usually formed near the base of the 
thallus and arise from the pericentral cells. In 
these corticate species the rhizoids are produced 
from the cortical cells. All the Polysiphonia 
species described in this paper are uncorticated. 
OBSERVATIONS AND RESULTS 
Polysiphonia ferulacea Suhringar in I. Agardh, 
Spec. Alg. 11:980, 1863 
Figure 1, A-E 
type: From the Atlantic coast of Mexico, 
North America, and presumed to be in the 
Agardhian herbarium, University of Lund. 
Thalli up to 5 cm in height, usually shorter. 
KEY TO THE HAWAIIAN species OF Polysiphonia 
1. Pericentral cells 4 2 
1. Pericentral cells more than 4 5 
2. Thalli chiefly erect; segments from as long as broad to 4 times as long as broad 3 
2. Thalli chiefly prostrate; segments half as long as broad Polysiphonia ferulacea 
3. Rhizoids cut off by a cross- wall from the proximal ends of the supporting pericentral 
cells 4 
3. Rhizoids not cut off by a cross-wall and produced from the central parts of the sup- 
porting pericentral cells Polysiphonia subtilissima 
4. Thalli rarely longer than 1 cm; segments about as long as broad . . . .Polysiphonia pulvinata 
4. Thalli more than 1 cm long; segments 2-4 times as long as broad Polysiphonia mollis 
5. Rhizoids multicellular; thalli less than 1 cm long; forming densely matted cushions 
Polysiph onia rhizoidea 
5. Rhizoids unicellular; thalli more than 1 cm long; forming loosely arranged tufts 6 
6. Pericentral cells 6; vegetative axes tapered Polysiphonia flabellulata 
6. Pericentral cells 10-12; vegetative axes approximately of equal diameter through- 
out Polysiphonia yonakuniensis 
