410 



BOTANY 



PART II 



determined the length on the coasts of California as 457 m. Other noteworthy 

 forms are the Antarctic species of Lessonia. in which the main axis is as thick as 

 a man's thigh ; from it are given off lateral branches with hanging leaf -like 

 segments. The plant attains a height of several metres, and has a tree-like habit 

 of growth. 



The Fucaceae ( 40 ), although relatively large, do not compare with the Lami- 

 nariaceae in size. As examples of well-known forms of this order may be cited 



FIG. 35Q.Macrocystispyrifem, Ag. , Younger, b, older 

 thallus. ( s ' 5 nat. size. After SKOTTSBERG.) 



Fucus vesiculosus, which has a ribbon-shaped, 

 dichotomously - branching thallus with air- 

 bladders, Fucus platycarpus without bladders, 

 and Fucus serratus (Fig. 352) with a toothed 

 thallus. They are fastened to the substratum 

 by discoid holdfasts, and growing sometimes 

 over 1 metre long are found covering extended 

 areas of the littoral region of the sea-coast. 

 Sargassum, a related genus chiefly inhabiting 

 tropical oceans, surpasses the other Brown 

 Seaweeds in the segmentation of its thallus. 

 The thallus of Sargassum shows, in fact, a 

 distinction into slender, branched, cylindrical 

 axes with lateral outgrowths, which, according 

 to their function, are differentiated as foliage, 

 bracteal, or fertile segments, or as air-bladders. 

 The species of Sargassum which in the 

 warmer regions of the ocean often form large 



yellowish-brown floating masses are worthy of note. In the Sargasso Sea of the 

 Atlantic Ocean there are according to BORGESEN two species (S. natans = S. bacci- 

 ferum and S. fluitans) which have this exclusively pelagic mode of life. They 

 have reproduced here for ages by vegetative budding, though originally coming 

 from attached species of the coasts of the West Indies and tropical America ( 41 ). 

 S. natans also occurs in the Pacific. 



The cells of the Phaeophyceae ( 42 ) have usually but one nucleus. 

 They contain a larger or smaller number of simple or lobed, disc- 



FIG. 351. Laminciria Cloustoni, Xorth 

 Sea. (Reduced to J.) 



