PREFACE 



In Physics, Chemistry and Mineralogy the properties of the 

 objects are measured and expressed by means of figures called 

 constants. A constant is independent of any theory : it is the 

 exact expression of a fact. The constants are in reality the 

 material by means of which theories are built up, the explana- 

 tion of the observed facts is found and the road opened for 

 new discoveries. 



In Botany and Zoology, on the contrary, the properties 

 (characters) of the living things are usually described by means 

 of terms. We say that a given object is long or short, broad 

 or narrow, oblong or oval, etc. Much progress would be 

 rendered possible if such terms as long, broad, short, etc., were 

 replaced by figures. This would be simple enough if the 

 properties of animals and plants were invariable. Unfortunately 

 these properties are almost always variable, not only within 

 the limits of one species, but also among the children of the 

 same parents and even among the progeny of one parent.^ 

 Variability has been hitherto the great obstacle which has 

 rendered impossible the general use of quantitative data (figures) 

 in Biological Sciences. 



The object of the present book is to describe a method by 

 which biological constants may be established. 



In the first two chapters I have expounded certain theoretical 

 views about the notion of species and variation. Those views 

 afford us a guide for the discovery of the primordia (simple or 

 elementary properties or characters) which are to be measured 

 in order to find constants. The constants themselves are, 

 however, entirely independent of any theory and of any 



^ Parthenogenesis, apogamy, asexual multiplication in animals and plants. 

 V 



