IV. FUCACE^. 55 



The geographical range of the Order Fucacece is very extensive. The great bulk 

 of the species occur within 35° of the equator on either side, within which limits 

 also the generic types are most varied. To the north of 35° Sargassa become rare, 

 and on the American shore the highest limit attained by any of this genus is in 

 Long Island Sound, about 44°. Beyond this limit the genus Fucus becomes the 

 prevalent form, and in the extreme north Himanthalia appears. Cystoseira, Avhich 

 has many representatives in the south of Europe, four of which extend as far as 

 Great Britain, is not found on the eastern shores of America, and but slightly, 

 represented on the north western. It forms an intermediate link, in structure and 

 distribution, between the tropical and arctic forms of the order. Very few species 

 have been traced into the Antarctic Ocean, where the most remarkable form is the 

 gigantic Durvillcea, which has a stipe and habit resembling a Laminaria ; or it may 

 be likened to a great Palm-leaf. The shores of Australia are peculiarly prolific in 

 plants of this order, and the species of that sea are remarkable as well for their 

 beauty, as for the large number of generic types which they exhibit. It is on 

 those shores that the most fully organised types of the olive-coloured Algae are met 

 with. 



In an economic point of view, the Fucacece take a high place among sea-plants. 

 Their ashes contain a large quantity of carbonate of soda, for which the Fuel were 

 formerly very much sought after, and even cultivated on some parts of the coasts of 

 Scotland where they did not grow naturally ; — rocks being deposited to attract them 

 to pebbly or sandy shores. At one time the proprietors of sea-shores on the most barren 

 islands of Scotland drew a very large revenue from the sale of the wrack (varec) 

 or sea- ware, which was then burned and its ashes sold under the name of Kelp:* 

 but improvements in chemistiy, by which carbonate of soda is now cheaply obtained 

 from other sources, have almost destroyed the kelp trade. These seaweeds are 

 now collected chiefly for manure, for which purpose they are often very valuable. 



Iodine is their most remarkable constituent, and is found in their tissues in 

 greater quantity than in any other of its known sources. The increasing demand 

 for this valuable substance may, therefore, be expected to cause a partial revival of 

 the kelp trade. 



The ordinary species, F. vesiculosus, is eagerly eaten in winter by Scotch and 

 Norwegian cattle, which regularly come down to the shore to browse on it at 

 the recess of the tide ; and Linnteus tells us that in Gothland the peasantry boil 

 it, and adding some coarse flour, give it to their hogs. 



SYNOPSIS OF THE NORTH AMERICAN GENERA. 



* Frond branched, leafy. Air-vessels stalked^ separate. 

 I. Sargassum. Receptacles racemose, in the axils of the upper leaves. 



* See Introduction, supra, p. 35. 



