APPLICABILITY OF A COEFFICIENT OF CORRELATION 341 



highly differentiated from those developed after growth is resumed as 

 an independent organism. 



Those rare cases in which the number of leaf homologs which are laid 

 down during the development of the seed is highly variable seem to 

 offer especially favorable opportunities for the morphologist to learn 

 something of the interrelationship of the two forms which may be 

 assumed by homologous organs. 



Suitable material for such work is furnished by a race of Phaseolus 

 mtlgaris (HARRIS 1916 b) having a modal number of four cotyledons 

 and four primordial leaves, but highly variable in the number of both 

 of these organs. 



The correlations and regression equations are : 



Correlation between number of cotyledons and number of leaves : 



Less mature series, r = .1170 .0320. 



c = 3.4759 + 0- 42i / 



/ = 3.2919 + 0.3252 c 

 More mature series, r = .1568 .0236. 



c = 3.5128 + 0.0499 I 



I = 3.0039 + 0.4922 c 

 Combined series, r = .1386 .0193. 



c = 3-5030 + 0.0464 / 



*== 3-3565 + 0.4142 c 



The correlations between number of cotyledons and number of pri 

 mordial leaves indicate slender interrelationships in this newly originated 

 race between characters which are usually thought of as highly cor 

 related. 



Note from the equations that there is on the average a change of .3 to 

 .5 of a leaf for each variation of one cotyledon, but that there is a 

 change of only .04 of a cotyledon for a variation of one leaf. 



The results for the combined series are represented graphically in 

 diagram 4. Regression is for each character very nearly linear. 



Correlation between total leaf homologs and number of cotyledons : 



Less mature series, r = .4328 .0264. 



c- = 2.4595 + 0.1413 h 



The plants were graded in a less mature and a more mature series as a precau 

 tion against recording as primordial leaves those really developed subsequently to 

 the maturation of the seed. 



6 The following correlations are published here for the first time. 



GENETICS 3: Jl 1918 



