414 MARINE PLANTS. 



and so li\e approximateU in tlie same liyht as our land 

 plants, are. like them, screen. The further from the sur- 

 face the deeper the red becomes. But in narrow, rocky 

 cre\ices and caves, where the plants depend chiefly upon 

 indirect lii^ht, the red Alwae approach the surface. In 

 se^'eral of the Grottoes of Posilipo at Naples the 

 red Algae, which nsualK grow at a depth of bet\'\'een 

 160 to 200 feet in the open sea, can be gathered by 

 hand. The dark brown colour, b^' which many 

 Algae are characterised, does not serve the same pur- 

 pose as the red. It is supposed that this brown 

 colouring matter acts as a screen -and diminishes the 

 force of the sunlight. Thus the brown Sea -wracks of 

 the Mediterranean often grow up to the surface, and in 

 our Northern seas we lind at low tide quantities of 

 Fucus in the open air, braving the direct ra^s of the sun. 



These shade-loving Marine Algae are very sensitive 

 to bright light. ^Fhis was proved hv I^erthold who 

 found that at a depth of from 260" to 360 feet in tlie 

 Gulf of Naples there was too much light for them, and 

 the^' therefore suffered. 



At Capri Berthold obtained fine and well developed 

 Algae at a depth of from 400 to 430 feet, showing that 

 the lowest range of their habitat was not reached. 

 This is remarkable \\-hen we consider that great white 

 disks sunk into the Mediterranean, -when it is calm and 

 sunny, disappear from view at a depth of from 165 to 

 200 feet. 



It may be asserted that the deep sea fauna begins 

 ajopro.ximately where plant life ceases. It continues down 



