ORGANIC EVOLUTION 



273 



ing off the classes-upon the ordinates and the frequencies 



upon the abscissae. 



Then, if this work be done by a class, let the totals 



of all the individual 

 counts be represented 

 i n another curve, 

 plotted in another 

 color upon the same 

 square; this will, on 

 account of the greater 

 numbers, more truly 

 represent the normal 

 variation for the 

 species, and it should 

 be a closer approxi- 

 mation to the sym- 

 metrical and balanced 

 curve of distribution 

 of error. 



The record of this 

 study will consist in : 



i) A drawing of a 

 variant showing the 

 normal condition for 

 the species, labelled 

 with the name, and 

 showing clearly the 

 parts counted and 

 plotted. 



2) The individual and collective curves of variation. 

 Mutation. — Variations are not all so Hght and inconstant. 

 Figure 167 shows a variant of the common Hnaria (L. vul- 

 garis, "butter and eggs"), the ordinary flowers of which are 



Fig. 167. A probable mutant of Linaria (L. 

 vulgaris) , "butter-and-eggs." 



