268 BOTANY. 



time, and the former gather around the inactive oospheres 

 in great numbers, and by the vigor of their movements 

 sometimes actually give them a rotatory motion (///, Fig. 

 182). The result of the coming together of the spermato- 

 zoids and the oospheres is the fertilization of the latter, and 

 their transformation into oospores by the secretion of a wall 

 of cellulose on each one. There is thus seen to be a close 

 similarity between the fertilization of Fucus and of other 

 Oosporeae ; particularly does it call to mind the sexual pro- 

 cess in Volvox and its allies. When, however, the sexual 

 organs proper, and their accessory organs, the conceptacles, 

 are taken into the account, the relationship of Fucus to Volvox 

 is seen to be much less than it appears to be at first sight. 



355. The development of the oospore takes place at 

 once ; it lengthens and undergoes division into numerous 

 ceils, and at the same time it elongates below into root-like 

 processes, which serve to hold fast the new plant (V, IV, 

 Fig. 182). There is a gap in our knowledge of the life- 

 history of these plants, extending from the young thallns to 

 the fertile plant ; probably when that is filled some plants 

 now supposed to be distinct will be found to be forms or 

 stages of these. 



(a) It is impossible, with our present knowledge of the structure of ap- 

 parently allied groups, to determine the limits of this class. It is prob- 

 able that it will eventually be shown to include most of the orders 

 usually arranged by English botanists under the Melnnospeniiece (the 

 Fucoidece of Agardh) ; should this surmise prove to be correct, Agardh's 

 name should be applied to the class in place of Fucacea, which should 

 be retained for the order. 



(b) The PhcBogporece, wliich are apparently allied to the Fucaceff, 

 are frequently of large size ; they are often flat, strap-shaped growths, 

 as In Lnminaria, of several metres in length ; in other cases they bear 

 bladders of enormous size (two metres long), ns in Nereocystis ; while 

 in Lessonia they assume tree-like forms, sometimes from eight to ten 

 metres (25 to 30 feet) in height, with a trunk ten to twenty centimetres 

 (4 to 8 inches) in diameter. Afacrocystis produces an enormous thallus 

 sometimes more than one hundred metres long (300 feet), resembling, 

 a gigantic pinnate leaf, which floats in the water by means of numer- 

 ous air bladders ; the whole is attached to a slender stem, one to two 

 centimetres thick. 



(e) The principal genera of F'/cacece are Fucus and Sargassum. Of 



