Individual Strength and Length of Fruit. 531 



Maximum and minimum simply refer to the len^^h 

 of the longest and shortest fruits. M is Galton's methan 

 or the mean — the value of which half tlie individuals do 

 not attain, but is exceeded by the other half. 



This median is found by interpolation, on the assump- 

 tion that the fruits measured as 24 mm. varied contin- 

 uously between 23.5 and 24.5 mm. Qo and Qp are the 

 ordinates which are separated from M by a quarter of 

 all the individuals in each case. They are also found by 

 interpolation. 



Galton^s quartiles are therefore: Qi = M — Qo and 

 Q^ = Qp—M. Further (Oi + Q2)/2 = Q is the measure 

 of the amplitude of the curve. Lastly Q/M is a measure 

 of this value independent of the size M and of the nature 

 of the variable character; a number therefore by means 

 of which the variation of the fruit length in Oenothera 

 may be compared with the variation of other characters 

 in other plants. 



These values calculated from the above data are as 

 follows : 



Qt Q2 Q % 



1.9 2.0 1.95 0.08 



In the description of the experiment Qo and Qp can 

 be omitted, now that the values 0\, M and O2 have been 

 calculated from the empirical data. 



A greater degree of accuracy can be attained in these 

 investigations by determining the mean length of the 

 fruits on a given plant instead of determining that of a 

 single fruit only. The question then arises : from how 

 many fruits should this mean value be calculated. I ha\e 

 measured five; and in this section and in the following 

 one I have used the mean of the lengths of the lowest 



