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1925] Setchell-Gardner : Melanophyceae 629
character of the attaching portion—"rhizome" and hapteres. In the
deep sea species, there is no rhizome and the mass of hapteres developed
often becomes several decimeters in thickness and up to a meter in
diameter, while in the shore species the conspicuous '
' rhizome '
' is flat
and adheres closely to the rock, dying and decaying at the rear as it
advances and spreads out in all directions. We have had an excellent
opportunity to study what might be considered a natural experiment
upon the effect of changing the deep sea species to the habitat of the
shore species at San Pedro, where a government breakwater was
extended out from the shore a long distance in the vicinity of a large
"kelp bed" of Macrocystis pyrifera. Thousands of plants attach
themselves to the rocks along low-tide level and persist until they are
torn loose. In not a single instance has the nature of the holdfast
been changed. It thus seems perfectly definite that the shore species
is a distinct entity, as well as the deep sea species. We have never
seen any specimens of either species which would seem to represent
transition stages between the two.
53. Pelagophycus Aresch.
Holdfast of several whorls of strong, dichotomously branched
hapteres diminishing in size toward their termini ; stipe solid at the
base, hollow above, constricted at the summit just below the large
spherical bladder, again becoming smaller and solid for a few centi-
meters beyond the bladder at its summit, dividing once dichotomously,
each branch again dividing unilaterally 4-6 times and each branch
bearing a single large terminal blade.
Areschoug, in Botaniska Notiser, 1881, p. 49 ; Observ. Phycol.,
part 5, 1884, p. 6.
Pelagophycus is one of the large, conspicuous, monotypic kelp
genera confined to a relatively small area on the Pacific coast of North
America. Its resemblance to Nere&cystis is striking so far as the main
stipe up to the first dichotomy is concerned. Above the first, or occa-
sionally, the second dichotomy, however, the unilateral splitting and
sympodial character of the stipe clearly places the genus with the
Macrocysteae.