ECOLOGICAL 107 



teristic of the World of Life. The first four that we shall mention 

 are on a somewhat different plane from the others, being more 

 fundamental, almost like biological axioms. 



(i) There is the fundamental balance between animals and green 

 plants. For green plants by their photosynthesis make food for 

 themselves and for the animals that are directly or indirectly 

 dependent on them for sustenance. Moreover, to the photosynthetic 

 process we owe most of the oxygen of the air, on which almost all 

 life depends. 



(2) Then there are the nutritional chains that bind different 

 organisms into a sequence of re-embodiments. Thus Diatoms and 

 Peridinid Infusorians form the food of the Copepod Crustaceans 

 of the open sea; these form the staple food of mackerel; which may 

 be eaten by man. As we have mentioned elsewhere, a pound of 

 cod's flesh requires for its making ten pounds of large whelk or 

 "buckie", each pound of which corresponds to ten pounds of sea- 

 worms, each poimd of which corresponds to ten pounds of ani- 

 malculae and organic particles. So that a pound of cod's steak 

 represents a thousand pounds of "sea-dust". 



(3) From these two fundamental facts it follows that there will 

 be many minor instances of balance, to some of which we have 

 referred in the section on the Balance of Nature. Thus in a given 

 region there will be an estabHshed balance between the carnivores 

 and the herbivores, between the insectivorous birds and the insects, 

 and so forth. 



(4) Of great importance are the linkages effected by help of 

 Bacteria, which complete many a circle both on land and sea. 

 The dead body of the animal or of the plant is decomposed by 

 certain putrefying Bacteria, and there is a liberation of water, 

 carbon dioxide, and ammonia, all of which may be re-absorbed by 

 plants and used over again. In many cases, the ammonia, formed 

 by the putrefaction of the proteinaceous substances of the dead 

 organism, is changed by specific Bacteria into nitrites, which are 

 changed by others into nitrates, and these, absorbed by the roots, 

 form the ordinary source of nitrogen for green plants. These plants 

 are eaten by animals, and so the world goes round. Liebig was one 

 of the first to have a clear view of this circulation of matter. 



(5) In various ways in the course of evolution one living creature 

 has become dependent on another for the continuance of its race. 

 Thus many flowering-plants cannot produce fertile seeds unless the 

 appropriate insect-visitor dusts the stigma with the pollen carried 

 from the stamens of another blossom of the same species. Similarly 

 with the scattering of seeds by birds and by some mammals; the 

 necessary sojourning of the larva of the freshwater mussel in some 

 fish like the minnow, and of the young of the Bitterling (a Continental 

 freshwater fish) in the gill-plate of the mussel; and the indispensa- 



