FUCACE^. 13 



The Fucaceae are readily known from all other olivaceous 

 sea-weeds by a character at once natural and easily ascer- 

 tained, namely, the position of their spores within little hol- 

 lows sunk in the substance of the plant, and communicating 

 with the surface by a pore. 



This order is much the most extensive among Melano- 

 sperms, comprising within its limits upwards of 230 species, 

 which is about equal to the contents of all the other orders 

 of this division put together. More than half of them belong 

 to the genus Sargassum, and the rest are distributed among 

 22 or 23 generic groups, varying in the number of their spe- 

 cies from I to 20. The order is represented in most climates 

 from high northern and southern latitudes to the equator, 

 but the number of generic forms is much greater between 

 the parallels of 30° and 40°, and the number of specific 

 forms greater within 30 degrees of the equator on either side. 

 Very few vegetate in the polar regions of either hemisphere. 

 In the north the species of Fucus and Himanthalia alone 

 reach to the Icy Sea ; and in the Antarctic Ocean the order 

 is limited to Durvillcea, a genus of gigantic growth, resem- 

 bling Laminaria in outward character, and to ScytothaUa 

 Jaquinoiii, a fine Alga allied to sub-tropical forms. The 

 British species, excluding three doubtful natives, are but 

 fourteen, yet from the strictly social habits of several of them 

 they cover more surface of tidal rocks than all the other 

 Algse put together. It is these plants which impart the deep 

 brown colour to the belts of rock exposed on the recess of 

 the tide. The species of warmer latitudes are much less 

 striking to a casual observer, as they rarely occur in masses, 

 but are more usually dispersed here and there in the recesses 

 of rocks; thus, though the number and variety of species are 

 greatly increased, the general effect to the eye is diminished. 

 The chief centre of the order seems to be along the shores 

 of New Holland, Tasmania and New Zealand, where the ge- 

 neric types are most numerous, and the external characters 

 of the frond most varied. In Sargassvm ^ which extends at 

 either side of the line to the parallel of 45°, and gradually 

 increases in number of species towards the equator, we have 

 the most perfect type of frond which the order affords. In 

 this genus there is a regular distinction of parts into stem, 

 branches, leaves and inflorescence : the leaves in most spe- 

 cies furnished with a midrib, and developed in a sub-spiral 

 order, like those of more perfect plants. 



In an officinal point of view the Fucaceae are among the 



