20 AEKIV FÖR BOTANIK. BAND 12. N:0 1^. 



These numbers give: 



Pistil 



M = 4,36 ± 0,12 

 (7 = 0,50 ± 0,08 



g: M = 0,11. 

 Stigyna. 



M = 0,291 ± 0,017 

 a = 0,045 ± 0,012 



(7 : if = 0,16. 



Both measures were performed with the ocular-micro- 

 meter. 



C) Correlation. I have examined above some cases of 

 correlation belonging to the dominion of homograde stati- 

 stics, as the correlation between the number of flower-stalks 

 and the number of leaves in the rosule, the correlation 

 between the thickness of the stem and the number of flower- 

 stalks and other similar questions. In those cases it was 

 stated that a correlation between two characters did exist, 

 but no numerical measure of the degree of that correlation 

 was given. It is, indeed, not impossible to find such mea- 

 sures, but either are they in many cases somewhat arbitrarily 

 chosen or, in others, mathematically more intricate to cal- 

 culate and I have left them here out of consideration, con- 

 fining me to such elementary methods as are given in the 

 »Grunddragen». 



In heterograde statistics such a measure of the degree 

 of correlation between two characters is well defined and 

 easy to calculate numerically. It is the so called coefficient 

 of correlation (r). I give beneath the value of this coefficient 

 for 5 pairs of characters of Trientalis europaea. 



15. Correlation between the length of the stamen {s) and 

 the length of the pistil {p). There were only 13 simultaneous 

 values of s and p. 



