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 (III, 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 

 cells, 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 thallus 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) The principal genera of Fucacece are Fucus and Sargassum. Of 

 the first, F. nodosus, F. furcatus, and F. ve&iculosus are the most 

 common species on our Eastern coast; the latter also occurs on the 

 Pacific coast; both are known as Rock-weeds. Sargassum vulgare is 

 common on the Atlantic coast ; 8. bacciferum, the Gulf-weed, is 

 found in the warmer parts of the several oceans, and in mid- Atlantic 

 covers an immense tract known as the Sargasso Sea. 



(b) The species of Fucus and Sargassum are washed ashore in great 

 quantities during violent storms, constituting the bulk of the 



wrack " of the coasts. They furnish valuable manure for enrich- 

 ing the soil, and are largely used for this purpose. From their ashes 

 alkalies and iodine are obtained. 



(c) In the Silurian period Fucoides anliqum represented the order 

 Fucacese. In the Devonian period the order was abundantly repre- 

 sented. Fucus, Sargassum, and other genera were already in exist- 

 ence during Tertiary times. 



