CHAPTER TV 
SOME INTER-RELATIONS OF PLANTS AND ANIMALS 
THE most important and fundamental difference 
between the animal and plant worlds is this: plants 
possess the power of manufacturing their food out of 
the inorganic materials of which it is composed, while 
animals cannot do this. Give an ordinary plant access 
to water with a pinch of mineral salts in it, to the air, 
and to sunlight, and by the agency of chlorophyll—the 
green colouring-matter of the leaves—the miracle will 
be accomplished, and dead materials transformed into 
living substance. - Animals, on the other hand, are de- 
pendent for their food-supply on organic material— 
that is, on either plant or animal substances; and since 
they cannot live by taking in each other’s washing— 
in other words, by eating each other—it follows that 
the animal world is dependent on the plant world for 
its continued existence. A porpoise may live on 
herrings, herrings on small fry, fry in turn on minuter 
organisms, and so on down the scale; but their ulti- 
mate source of food is the tiny Algz which swarm in 
the water—the Plankton in Hensen’s original sense— 
which, alone in this chain, can build up their bodies out 
of the sea and air. That these minute plants can sustain 
the enormous drain upon them due to their use as a 
food-supply by myriads of larger organisms is due to 
their vast numbers and rapid increase. Sea-water 
a 
