86 BOOTS OP SEA- WEEDS ACT AS HOLDFASTS. 



each of which takes a separate gripe of the rock, by the 

 disc at its extremity, and all combined form a conical 

 mass, representing the simple disc of the Fuci and most 

 other sea-weeds. On some sandy shores, there are sea- 

 weeds with much more extensive roots, roots that re- 

 semble those of grasses which cover sand-downs, extend- 

 ing to a considerable depth in the sand, branching out 

 in every direction, and forming a compact bed of fibres, 

 and a firm foundation for the vegetation. Such roots 

 are obviously induced by the nature of the soil on which 

 the plant grows, and would be superfluous on a rocky 

 bottom. 



The roots of sea-weeds seem to be little concerned in 

 the active growth of the vegetable, except in the earlier 

 stages. Like all the lower vegetables included in the 

 class Cryptogamia, the sea-weeds are composed of a sim- 

 ple aggregation of cells,* which form a more of less ho- 

 mogeneous body through which fluids freely pass, and 

 whose whole surface absorbs nourishment from the sur- 

 rounding water. This is the reason why the geological 

 nature of the district has little relation to that of the 

 marine vegetation which clothes the rocks. But the 

 character of this vegetation is greatly varied by the out- 

 ward form of the rocky masses. Thus, on a shore com- 

 posed of granite-rocks, where the masses are rounded and 



* A cell, in botanical language, means a little bag-like body, com- 

 posed of membrane, and containing a living substance capable of spon- 

 taneous growth by multiplication or division of its parts. Of such 

 little bodies, millions of which may be contained within a cubic inch, 

 all the soft parts of vegetables are composed. In sea-weeds the cells 

 are often of large size. 



