52 



Mutability and Individual Variation. 



races is due. But we must not forget, what we have 

 ah'eady mentioned,^ that the word "race" is used here in 

 a different sense from that in which it is used in anthro- 

 pology. The principal difference between the so-called im- 



2lMm22 23 Zii 



26 27 2a 29 



it 32 33 3<> 



Fig. 13. Exhibition of Variability by the Fan Type of Plotting.^ 



proved races on tlie one hand, and varieties, subspecies, 

 elementary species, incipient species and so forth, on the 

 other, will form the subject of our third chapter. 



^ See page 41. 



^ VariabiHty can be exhibited by other means than l)y Quetelet's 

 curve (Fig. 10) or Galton's Ogive (Fig. 11). If it is a question 

 of comparing successive generations with one another the "fan" 

 type of presentation (Fig. 13) is to be recommended. The point 

 from which the rays emanate gives the character of the mother 

 plant. The length of the base of each triangle on the upper hori- 

 zontal line gi\'es the length of the ordinates in an ordinary curve, as 

 they are drawn above in the diagram. This breadth gives at a glance 

 the frequency of individuals for any one scale character. The data 

 for this figure consist of measurements of the length of the ripe 

 fruits of Oenothera Lamarekiana taken in the year 1891 (99 fruits 

 measured in whole millimeters). The lengths were distributed in 

 the following way over the fruits: 



mm. 21 22 23 24 25 26 27 28 29 30 31 32 2)2) 34 

 I I 7 8 14 15 12 13 5 7 5 4 4 3 

 The crooked line follows Quetelet's law (a-J-Z?)". 



