224 THE INDUCTIONS OF BIOLOGY. 



equilibrium ; that if tliey are not united, this equilibrium 

 ends in dissolution ; but that by the mixture of them, this 

 equilibrium is destroyed, and a new evolution initiated. 



§ 78. What are the conditions under which Genesis takes 

 place ? How does it happen that some organisms multiply 

 by homogenesis, and others by heterogenesis ? Why is it 

 that where agamogenesis prevails, it is usually from time to 

 time interrupted by gamogenesis ? These are questions of 

 extreme interest ; but questions to which decisive answers 

 cannot yet be given. In the existing state of Biology, we 

 must be content if we can learn the direction in which 

 answers lie. A survey of the facts, discloses certain correla- 

 tions which, if not universal, are too general to be without 

 significance. 



Where the multiplication of individuals is carried on by 

 heterogenesis, we find, in numerous cases, that agamogenesis 

 continues as long as the forces which result in growth, are 

 greatly in excess of the antagonistic forces. While conversely, 

 we find that the recurrence of gamogenesis, takes place when 

 the conditions are no longer so favourable to growth. In 

 like manner, where there is homogenetic multiplication, new 

 individuals are usually not formed while the preceding in- 

 dividuals are still rapidly growing — that is, while the forces 

 producing growth exceed the opposing forces to a great extent,* 

 but the formation of new individuals begins when nutrition 

 is nearly equalled by expenditure. To specify all the facta 

 !;hat seem to warrant these inductions, would take more space 

 than can be here spared. A few of them must sufilce. 



The relation between fructification and innutrition, among 

 plants, was long ago asserted by a German biologist — by 

 Wolff", I am told. When, some years ago, I met with the 

 assertion, I was not acquainted with the evidence on which it 

 rested. Since that time, however, I have, when occasion 

 favoured, examined into the facts for myself. The result has 

 been a conviction, strengthened by every further inquiry, 



