70 THE QUANTITATIVE METHOD IN BIOLOGY 



mechanical and chemical?- With regard to cell-division (which 

 is the simplest case of division), BATESON divides the 

 mechanical variations in their turn into two groups: (i) the 

 division properly so called and (2) the differentiation which 

 brings about difEerences between the parts produced by a 

 division. 



It is possible to go further along the line indicated by BATE- 

 SON. I want to expound this subject by means of examples. 

 In the present work I limit myself almost entirely to the vege- 

 table kingdom because at the time being the notes about the 

 properties of animals, which I have collected for years, are not 

 within my reach. 



The researches the results of which are partly expounded in this book have 

 occupied about thirty-five years. I began with measuring various objects 

 taken at random among animals and plants, following the ordinary statistical 

 method initiated by QUETELET. I submitted my first results (asymmetrical 

 and multi-humped curves) to several biologists and mathematicians, who told 

 me that QUETELET'S attempts were foolish and I was wasting my time. 



Later I limited myself almost entirely to the measurement of various proper- 

 ties of numerous species of shells, and I spent several years before I could 

 find in a satisfactory way a sufficient number of primordia. I abandoned this 

 exceedingly interesting work because of the difficulty of obtaining the material 

 (numerous specimens of each species) I wanted for further methodical investi- 

 gation. (See § 89, third example.) 



After that I began the study of insects, and after a preliminary work which 

 lasted again several years I began in October, 1907, the methodical investiga- 

 tion of the species of the genus Carabus (including Calosoma) . This work was 

 continued till July, 1914, and interrupted by the war. 



§ 54.— FIRST EXAMPLE : SPIROGYRA.— I take as 

 example a specimen of Spirogyra (or Zygnema, or any other 

 alga consisting of a series of cells without branches) the 

 structure of which is very simple. This plant consists at the 

 beginning of one cell (zygospore, egg). By its form this young 

 individual resembles more or less an ellipsoid. Since we have 

 no exact information about its form, we caU it oblong or use 

 another rather vague term. Two simple visible properties may 

 be discerned here : length and breadth.^ Both ought to be 

 measured according to two rectangular axes : longitudinal and 

 transverse. 



At a certain moment the egg is divided into two cells : the 

 (imaginary) straight line which joins the centres of both new 

 cells is the line or axis of division (segmentation) ; this axis 

 coincides with the longitudinal axis of the egg. 



The two cells (unicellular individuals) remain connected to 



^ BATESON, using the terms actual composition of material (chemical 

 vafiations) , does not make any distinction between two notions which I look 

 upon as being different: (i) the composition of the living mixture; (2) the 

 chemical properties properly so called (abiotic chemical properties). (See § 8.) 



^ These properties are variable, just as almost all the further mentioned 

 properties. See, on the measurement of variable properties. Part VI. 



