Seaweeds and Leaf-green 



The great Sargasso Sea is supposed by some authors 

 to occupy an area as large as Europe, and to be formed 

 entirely of algal fragments torn by storms from the 

 coast-line. But the common Sargasso weed has not 

 yet been discovered anywhere on the shore-line of 

 America. It is well able to float, for it has hundreds 

 of little buoys about the size of a pea along its fronds. 

 Such seaweeds are undoubtedly dangerous to navigation, 

 for if twined round the screws or paddle-wheels they 

 might stop the engines suddenly and cause an explosion ; 

 but the lurid tales about its awful inhabitants and ancient 

 derelicts have not been scientifically confirmed. 



Great as must be the amount of shore seaweeds, they 

 are by no means the most important of the order. 

 Algas occur also in fresh-water lakes and in all kinds of 

 pools, rivers, streams, and rivulets. The bottom, if not 

 more than 30 feet deep, and the sides of all such fresh- 

 water surfaces, are usually densely covered with them. 



But the most important in the world of all algae are 

 those which are not attached to the shore at all, but 

 which float free in the water and are carried about by 

 the currents and tides. They occur in almost all fresh- 

 water lakes, and especially in the open sea. They are 

 perhaps less numerous in the " deep blue sea" far 

 from the coast-line, though even there they are by 

 no means entirely absent. 



This free-floating life of the ocean is usually called 

 plankton (the name includes the marine animalculae 

 which occur along with the seaweeds). They are 

 commonest at a short depth, though they have been 

 found 1000 feet below the surface. In the Arctic and 

 Antarctic Ocean depths of 120 to 250 feet seem to 

 yield the largest amount. 19 



One can obtain samples of this plankton by attaching 

 a small bag of miller's gauze to the taps of a sea-water 



36 



