THE OPEN SEA ype 
flea, second link; mackerel, third link; man, 
fourth link; and so the world goes round. 
This nutritive chain is interesting in theory, 
but it is also very important practically, for 
on the abundance of the floating sea-meadows, 
and the population of small animals which 
these support, there depends, in large meas- 
ure, the success of the fishing industry in 
northern seas. 
In addition to the microscopic plants there 
are in some places great masses of drifting 
seaweeds of a higher order. They sometimes 
occur in such enormous dense patches that 
they impede the progress of ships passing 
through them. ‘These seaweeds do not grow 
at the surface but on the sea-floor in the shal- 
low water region, and when they are torn off 
by the waves they are carried by currents far 
out to sea. They live for a considerable time 
floating at the surface with the aid of their 
numerous little bladders, but gradually they 
lose their vitality and finally sink slowly to the 
bottom. New clumps are continually being 
brought by the same currents, so that in some 
parts of the ocean seaweed is always present. 
The best known of these areas is the Sargasso 
Sea in the Atlantic, and the weed there har- 
