88 THE QUANTITATIVE METHOD IN BIOLOGY 



mentioned properties are variable within the hmits of a given 

 species: the method of measuring variable properties is ex- 

 pounded in Part VI. 



§ 73.— RAMIFICATION OF THE UNIAXIAL SYSTEM. 

 COMPLICATED CASES.— In Pseudochcete gracilis the ramifica- 

 tion of the uniaxial system is very simple : the whole plant x con- 

 sists of one uniaxial individual (creeping stem) A of the Jirst 

 order or generation and several individuals (erect branches) B of 

 the second order or generation. 



The system of ramification of innumerable plants, belonging 

 to various systematic groups, is based upon the same principles 

 as that of Ps. gracilis. 



EXAMPLE : A young tree (for instance, Fagus or Quercus) 

 X consists the first year of a simple stem A (uniaxial individual 

 of the first order or generation) divided into several segments or 

 internodes ^ which are segments or individuals ^ + 1. The 

 stem A produces by ramification uniaxial individuals (branches) 

 B of the second generation, divided in their turn into internodes 

 B + 1. When this state is reached the young tree x is compar- 

 able to a Ps. gracilis (each internode taken as a whole being 

 "comparable to a cell). 



The branches B may produce in their turn individuals 

 (branches) C, and so on. Along each branch (axis) the branches 

 of the next generation and the internodes may be numbered 

 from the base to the summit. Whatever may be the number 

 of generations, branches and internodes, each individual (stem, 

 branch, internode) has a definite place in the society of sub- 

 ordinate individuals which is called a tree. 



The differences between the individuals (stems, branches, inter- 

 nodes) which are associated in a given tree ^ depend on their 

 position^ — that is to say, on social causes. I leave out of account 

 the differences brought about by external causes— for instance, 

 temperature, rainfall, light, shade, etc., which influence the 

 primordia of each segment during their sensitive period. 



(See, on this subject, §§ 59 and 66.) 



In any ramified plant we find a large number of simple 

 properties, which may be distinguished and classified according 

 to the scheme in § 72. 



The ramification of a uniaxial system does not only produce 

 branches properly so called, but cauloms and phylloms of various 

 kinds (leaves, phyllodes, cladodes, scales, glumes, sepals, petals, 



1 An exact definition of the limit between two internodes is a rather subtle 

 morphological question. With regard to the application of the quantitative 

 method, the usual empiric and somewhat conventional definition of this limit 

 may be adopted. 



2 In other words, the individual variation within the limits of one specimen 



