ZOOGENESIS 



falling of the leaves in autumn and at the beginning of 

 the dry season, and more or less constantly at other 

 times as well, means the accumulation of a vast 

 reservoir of foodstuffs for anything capable of making 

 use of it. 



Bacteria and fungi thrive on this detritus, and earth- 

 worms and many other kinds of snails and slugs and 

 insects, as well as other creatures, feed either on this 

 decaying vegetation, or on the bacteria or fungi in it, 

 or on the living things that feed on them. 



Much of this material is consumed where it lies 

 upon the ground, but a vast amount is washed into 

 the rivers, especially by the floods of spring and at the 

 breaking of the rains, and is carried to the sea. A 

 large part of this is still in a condition to be eaten by 

 detritus feeding animals, while a great deal more, 

 especially in the form of organic substances in suspen- 

 sion or solution, is available as food for the ma- 

 rine plants. 



Our knowledge of the origin of the substances on 

 which the plants of the sea depend for their existence 

 is rather vague. But the evidence seems to indicate 

 that very largely, possibly for the most part, life in 

 the oceans is dependent, through the necessities of the 

 ocean plants, on food substances brought down from 

 the exposed land areas. 



The plants of the sea, at least those which support 

 the greater part of the ocean's animal life — minute 

 free floating plants invisible to the naked eye (cf. 

 fig. 86, p. i6i) — seem to require the presence in the 

 water of something that comes to them from the land. 



[4^] 



