aphotic

As experiment has shown that light waves capable of effecting chemical changes do not penetrate the water deeper than 400 meters and as the other conditions of assimilation are met above this line, it is proposed to distinguish a diaphanic region including the land and the water to a depth of 400 m. and inhabited by assimilating organisms and an aphotic region including the ocean and lakes below the assimilation-line and the dark caves of the crust, where plant life is impossible.