36 THE WORLD OF THE SEA. 
flat pipe, another a fine twisted thread. With these floating alge 
many marine plants which grow on the ocean bed are mixed. 
They become detached by the waves, and their air-cells cause the 
loosened branches to rise to the surface. M. de Martius thinks that 
many of the floating sea-weeds are uprooted by the whaies. When 
once at the surface, the fuci throw out branches and lobes 
and interlace with each other in every direction. These plants 
at the surface have such an exuberant growth that they may 
even be said to surpass in development the Axacharis Canadensis, 
a weed indigenous to the waters of the North American con- 
tinent. It was accidentally transported to this country about the 
year 1842; it has already spread over the greater part of England 
