SECT. 1 



CRYPTOGAMS 



367 



I 



of 2-25 m., ami, according to Skottsherg (^^), is at first dichotomously branched. 

 Single shoots of the thallus grow to the surface of the water, and floating there attain 

 a lengtli of 70 ni. ; they bear on one side long flat lobes divided at their free ends, 

 and having at the base of each a large swimming bladder. Other noticeable forms, 

 on account of their tree -like character, are the Antarctic species of Lessonia, in 

 which the main axis is as thick as a man's arm : from it are given off lateral 



-«/ 



Fig. 2S0. — Mcu.rorijstis pi/rifera, Ag.; a, 

 younger, h, older thallii.s. (After 

 SKOfTSBERi;. s'n iiat. size.) 



branches with hanoiug leaf-like segments. The 



,\ 



/ /. 



/ 



plant attains a height of several metres, and 

 has a tree-like habit of growth. 



Tiie Fucaceae, although relatively large, do 

 not compare with the Laminariaceae in size. 

 As examples of well-known forms of this order 

 maj- be cited Fncus vcsiculosus, which has a 

 rilibon-shaped, dichotomously branching thallus 

 \\ith air-bladders, Fucus platycarpus without 

 bladders, and Fucus serratus (Fig. 291) with 

 a tootlied thallus. They are fastened to the 

 substratum by discoid holdfasts, and growing 

 sometimes over 1 metre long, are found cover- 

 ing extended areas of the littoral region of the 

 sea-coast. Sarcjassum, a related genus chiefly 

 inhabiting tropical oceans, surpasses the other 

 Brown Seaweeds, and even all other Algae, 

 in the segmentation of its thallus. The thallus of Sarcjassum shows, in fact, a 

 distinction into slender, branched, cylindrical axes with lateral outgrowths, which, 

 according to their function, are ditierentiated as foliage, bracteal, or fertile seg- 

 ments, or as air-bladders. 



Sargassitm hacciferum, which in the warmer zones of the oceans, especially the 

 North Atlantic, occurs in large yellowish-brown floating masses (Sargasso Sea) is 

 worthy of special note. Hitherto it has been assumed that this plankton alga 

 grew attached on the coasts and had been detached by storms. According to 

 Sauvageav, however, it is probable that it has led for ages the life of a pelagic 

 sea-weed, reproducing only by vegetative budding (■'"'). 



Fir. 



290. — I.amiaaria Cloustoni, Xorth 

 Sea. (Reduced to J.) 



