24 THE WEALTH OF THE SEA 



growth. On this account practically all marine vege- 

 tation is near the surface, and the dark abysmal 

 depths of the sea are devoid of plant life, except 

 perhaps bacteria and other low fungoid forms. 

 Marine plants with very few exceptions are very 

 simple organisms. Seaweeds, or marine algae, al- 

 though resembling many land plants in appearance, 

 have nothing in common with the higher terrestrial 

 types, for they are composed of but one class of cells. 

 Algae have no roots in the true sense of the word, 

 for the holdfasts merely act as anchors, and do not 

 absorb nourishment from the sea bottom. The food 

 required by the algae is obtained by the individual 

 cells composing the plant from the substances held in 

 solution by the surrounding water. 



Although vegetable life is so exceedingly scarce 

 in the profound depths of the ocean, animal life, not 

 requiring light for its existence, is plentiful. Yet 

 it is not surprising that less than a century ago 

 scientists believed that life at great depths was 

 impossible, for in the deeper parts of the sea the 

 pressure is tremendous, and it is totally dark and 

 very cold. At a depth of a mile, the pressure amounts 

 to a ton to the square inch, yet with a perfectly 

 uncanny adaptability many species of delicately con- 

 structed animals thrive. Fish, tunicates, crustaceans, 

 mollusks, echinoderms, worms, coelenterates, and pro- 

 tozoa are found at great depths, but nearly all of 

 these are so modified, either in form or color, or in 

 the structure of their organs of sense, or in other 

 ways, that they can be recognized at once as deep- 

 sea animals. The enormous pressure of the great 



