674 Geological Periods of Mutation. 



1. The number of elementary characters of a higher 

 plant, that is to say, the number of mutations through 

 which its ancestors have passed from the beginning, is 

 probably not more than a few thousand. 



2. The a\'erage intervals of time between two suc- 

 cessive periods of mutation are similarly to ])e estimated 

 at a few thousand years. 



3. From this we may conclude that a period of some 

 millions of years is sufficient for the whole development 

 of the animal and vegetable kingdom ; or, in other words, 



4. The doctrine of mutation does not demand a longer 

 period for the duration of life than that which has been 

 given by Lord Kelvin, viz., 24 million years. 



These theses may be most simply summarized in the 

 statement that the product of the number of elementary 

 characters of an organism, and of the mean interval of 

 time between two successive mutations of its ancestors, 

 is equal to the extent of biological time.^ If we call the 

 former magnitude M (the number of mutations), the 

 length of the intervals L and biological time BT, we have 

 the expression 



X L = BT. 



I have called this the biochronic equation.^ It will, 

 I hope, help to demonstrate the importance of the doc- 

 trine of the elementary units of organisms, and thus 

 bring this doctrine prominently before the eyes of the 

 general reader, as well as of the trained investigator. 

 This is my main object in enunciating it. 



' The mutations referred to in these paragraphs are of course 

 progressive mutations. 



'Die Mutationcn und die Mutafioiispcrioden, p. 63. 



