OLIVE-GREEN AND BROWN SEAWEEDS 73 
F. serratus. Frond distinctly toothed or serrated along the margin; 
midrib conspicuous through the main axis and forked brauchings; no 
air-vessels. This species is rare on the Atlantic coast. (Plate XV.) 
F. furcatus. Frond narrow, tough, without air-vessels; regular 
forked branching; midrib distinct below, inconspicuous above; recep- 
tacles long, narrow, not inflated. Found from Boston northward. 
F. ceranoides. Frond flat, rather membranaceous, or less leathery 
than in the preceding species; repeatedly forked; midrib not running 
through every division; no air-vessels. (Plate XV.) 
Genus Ascophyllum 
A.nodosum. This species, formerly called Fucus nodosus, is next to 
Fucus vesiculosus the most common rockweed. Frond one to five feet 
long, dark brown, strap-like, leathery ; width of main stems one fourth 
of an inch or more, and uniform throughout; large, single, oblong air- 
vessels distend the frond at intervals. Branches of various length 
emerge from the sides of the main stem. Ovoid or ellipsoidal branchlets 
or receptacles, single or in groups, occur at intervals along the sides of 
both stem and branches. These fall off after a time and are found in 
quantities in tide-pools. (Plate XV.) 
Genus Phyllospora 
P. Menziesii. Branching holdfast; short stem which immediately 
divides into strap-like branches ; branches edged with leaves varying in 
length, rounded at top, narrow, stalked at base ; leaves placed at intervals, 
or crowded together, and interspersed with air-vessels which are often 
tipped with leaflets; stems expand at summit into leaf-like lamine and 
are edged with leaflets at the base; plant often one hundred and twenty 
feet or more in length; tough and leathery in substance. Very common 
on the California coast. (Plate XVI.) 
Genus Cystoseira 
C. expansa. Frond long, slender, repeatedly branched ; air-vessels 
ellipsoidal and “chained” together in the lower half of the branches. 
The plant grows in deep water, and shows iridescent colors when seen 
through the water. It is found on the California coast. 
Genus Halidrys 
H. osmunda, the sea-oak. Frond flat, alternately toothed or indented 
below; branched apex, bearing air-vessels like long-stalked pods ; sub- 
stance leathery. Found on the coast of southern California. (Plate 
XVI.) 
Genus Sargassum 
Sargassum is distinguished by its differentiation into stem and 
leaf, resembling in outward appearance the higher plants. It 
