70 MARINE ALG 
Genus Laminaria 
The plants of this genus are all large, varying from one foot to 
twelve feet or more in length. They are of wide geographical 
range, and are more numerous in species than any others of the 
order. They are commonly known as oarweeds, tangle, devil’s- 
aprons, sole-leather, kelp, sea-furbelows, and so on. 
L. longicruris (‘long-stalked”). Stem six to twelve feet long, one 
to two inches thick, slender and solid at base, hollow and inflated at the 
middle, contracted at the top; attached by a strong, branching, root-like 
holdfast ; color light brown. The large, single, leaf-like lamina, usually 
shorter than the stem, is five to twenty feet long, two to three feet broad, 
with much waved and folded margin, outlined with two rows of depressed 
spots. The spores form a band in the center of the blade. Found from 
Cape Cod northward and on the Pacific coast. 
L. saccharina, the sea-tangle. This species differs from L. longicruris 
in having a short, solid stem and narrow, ribbon-like lamina. Stem three 
inches to four feet long ; lamina three to thirty feet long, six to eighteen 
inches wide, with central band of depressed spots; margin much waved ; 
color olive-green, semi-transparent. It is named from the saccharine 
matter, called mannite, which it contains. Found on northern shores of 
the Atlantic and the Pacific oceans. (Plate XII.) 
L. digitata (“fingered”). Stem one to five feet long, thick, round, © 
and solid; lamina oval at base, leathery, smooth, brown, deeply cleft 
into segments of unequal breadth. It is named from the hand-like form 
of the lamina. This species is found in Long Island Sound, but is not 
common south of Cape Cod. The stem is used by fishermen for knife- 
handles. Pieces of it, placed on the blades while green, contract in dry- 
ing and become solid. (Plate XIII.) 
For the genera Macrocystis, Nereocystis, Lessonia, and Thalas- 
siophyllum, see the Introduction, pages 35, 36. 
ORDER DICTYOTACEA 
Genus Dictyota 
D. fasciola. Fronds olive-brown, expanded, membranaceous, erect, 
flat; many times forked narrow branches ; grows in tufts six to ten inches 
long, matted at the base. 
D. dichotoma. Same as D. fasciola, except that the divisions of the 
forked frond are one eighth to one half of an inch wide. Found in tide- 
pools in Southern waters. (Plate XIII.) 
GENUS Zonaria 
Z. lobata. Thallus flat, fan-shaped, but not so rounded as in Padina 
pavonia, twelve or more inches in height, cleft irregularly into many 
