OLIVE-GREEN AND BROWN SEAWEEDS 69 



the laminaB are perforated ; in Alaria there are wing-like leaflets 

 below the laminae. 



The Laminariacece and Fucacece are the seaweeds used in making 

 kelp. For this the algae 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 algse and many zoophytes 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. Ttirneri. 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 papillae 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.) 



