11. THE LENGTH OF THE FRUIT IX OENO- 

 THERA LAMARCKIANA. 



§ 3- CORRELATION BETWEEN INDIVIDUAL STRENGTH 



AND LENGTH OF FRUIT. 



Let us now consider the relation between the indi- 

 vidual strength of the plant and a character which can 

 be conveniently studied by statistical methods ; partly as 

 an example of the method of dealing with measurements, 

 described in the preceding chapter ; and partly on account 

 of the importance of the question itself. For this purpose 

 I have chosen, as I indicated in the previous section, the 

 length of the ripe fruits of our Evening Primrose (Fig. 

 114). 



These fruits are highly variable, not only in plants 

 treated differently but also in the various individuals of 

 the same culture. It is not difficult, as a rule, to find 

 among the longest ones individuals which have twice the 

 length of the shortest ones (Fig. 114 A and C). Such 

 fruits are however very rare; the intermediate ones (Fig. 

 114 B) are always by far the commonest. In sorting 

 such material we easily find that the frequency of the 

 various values is describable in terms of the Quetelet- 

 Galton law, especially when the number of plants meas- 

 ured is large. 



