OLIVE-GREEN AND BROWN SEAWEEDS 69 
the lamin are perforated; in Alaria there are wing-like leaflets 
below the lamine. 
The Laminariacee and Fucacee are the seaweeds used in making 
kelp. For this the alge are burned, and the ash is then separated 
into its different mineral constituents and used for various manu- 
facturing purposes. 
Genus Chorda 
C. filum. Entire frond cylindrical, divided internally by transverse 
septa; one fourth to one half of an inch in diameter, tapering at each 
end ; ordinarily one to twelve feet long, but sometimes attaining a length 
of forty feet. When young the frond is covered with fine, transparent 
hairs; later it is brown and leather-like. The growth takes place at the 
base, just above the disk-like holdfast, and at the apex it is constantly 
dying off. The species is common on Northern shores, at and below low- 
water mark. Often it is in masses which seem like meadows of waving 
grass under water. Various small alge and many zodphytes are to be 
found on the fronds. (Plate XII.) 
Genus Alaria 
This genus is readily distinguishable by the fact that it has 
leaflets below the lamina. It is found north of Cape Cod. 
A. esculenta. Stem compressed, four to twelve inches long, one 
fourth to one half of an inch wide, and running like a midrib through 
the lamina; lamina one to ten feet long, two to ten inches wide, fre- 
quently torn and ragged; margin wavy; leaflets three to eight inches 
long and without midrib, growing on both sides of the stem, below the 
lamina. The spores are produced in the leaflets in the autumn. This is 
an edible alga and is used as food in Scotland and Ireland, where it is 
called henware, badderlocks, murlins, and so on. (Plate XII.) 
GENUS Agarum 
The sea-colanders. 
A. Turneri. Stem two to twelve inches long, round below, flattened 
above, and extending like a midrib through the lamina; lamina one foot 
to four feet long, with holes over the whole surface; margin wavy. The 
perforations in the lamina are produced by conical hollow papille# which 
cover the young frond and which at length burst, leaving a hole which 
enlarges as the plant expands. This species is found from Cape Cod to 
Greenland. . 
There are other species, which differ from this one in the size of the 
perforations, the shape of the lamina, and the prominence of the midrib. 
Harvey describes the plant as an arctic genus growing ten to twelve 
feet long. (Plate XII.) 
