LAMINARIACEjE. 27 



expansion is sometimes ribbon-shaped, quite simple and ta- 

 pering to the extremity; sometimes it is cloven vertically into 

 many narrow segments; sometimes it is pinnatifid (as in 

 Ecklonia); and sometimes (in Agarum and Thalassiophyllum) 

 it is perforated like a sieve. In some it is ribless, in others fur- 

 nished with a more or less perfect midrib. Air-vessels often 

 absent; where they occur they are formed by swellings at the 

 base of the leaf, in the general stipes or in its branches. In 

 those species which are perennial the stipes lasts for several 

 years, but the leaf is changed at the end of each season. New 

 growth, therefore, commences at the apex of the stipes and 

 base of the leaf, and continues till the old leaf is gradually 

 pushed off. The fructification consists in innumerable mi- 

 nute spores, packed vertically together, in strata, extending 

 either over the whole surface of the plant or covering spaces 

 of the surface of considerable extent, In the simplest kinds 

 the whole frond becomes covered with spores (as in Chorda] ; 

 in more perfect genei'a indefinite cloud-like patches are dis- 

 persed over the leafy portion ; and in the most organized 

 examples (as Alaria) the spores form distinct sori of large 

 size, situated in proper leaflets. The spores are either sim- 

 ple, or contain, at maturity, four sporules. Very generally 

 they are stipitate, or taper at base into a more or less evident 

 pedicel, formed from the lower half of the sporular cell. In 

 some genera they are mixed with paranemata, among which 

 antheridia occur ; in others the whole stratum is composed 

 of spores. 



The plants of this family are almost all of large size, and 

 many of them gigantic, greatly exceeding in bulk any other 

 marine vegetables. The Oar-weeds and Tangle of our own 

 coasts have frequently stems six or eight feet long, and fronds 

 expanding from their summits to as great a length ; and the 

 sea-thong (Chorda) often measures forty feet in length. But 

 these dimensions are small compared with their kindred on 

 the shores of the Pacific Ocean. The Nereocystis, a plant of 

 this family inhabiting the north-western shores of America, 

 has a stem, no thicker than whipcord, but upwards of 300 

 feet in length, bearing at its apex a huge vesicle, six or seven 

 feet long, shaped like a barrel, and crowned with a tuft of 

 upwards of fifty forked leaves, each from 30 to 40 feet in length. 

 The vesicle, being filled with air, buoys up this immense frond, 

 which lies stretched along the surface of the sea : here the 

 sea-otter has his favourite lair, resting himself upon the vesi- 



