OLIVE-GREEN AND BROWN SEAWEEDS 73 



F. serratus. Frond distinctly toothed or serrated along the margin ; 

 midrib conspicuous through the main axis and forked branchings ; no 

 air-vessels. This species is rare on the Atlantic coast. (Plate XV.) 



jP. furcatus. Frond narrow, tough, without air-vessels ; regular 

 forked branching ; midrib distinct below, inconspicuous above j 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 laminae 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 



