154 Plant-Breeding 



which is multiplied by 4.17, found in column D 09 opposite 

 15.5. So the result is as follows : 



4.17+ l(-9.7) +l(-7.7)+ 1 (-5.7)+ l(- 



9(0.30) +6(2.3) +5(4.3) +2(6.3) +3(8.3) +3(10.3)+1(12.3) 



+ 2(14.3)+ 1(16.3) = 535.01. 



Having obtained all the numbers in the 2P column, the 

 sum is taken and the coefficient of correlation is found ac- 

 cording to the following formula : 



SP 



4402.54 



358(5.20) (5.23) 



Conception of unit-characters. Most recent studies are 

 analytical in their nature. We now conceive of plants 

 and animals to be composed of separately heritable units 

 known as unit-characters. It is not possible at present to 

 say exactly what a unit-character is, but we may call it 

 the smallest heritable part or attribute a plant may 

 possess. For example, the color of the flower, size and 

 shape of leaf, height of the plant, susceptibility or im- 

 munity to disease, and so forth, may be unit-characters. 



Knowledge of heredity has come through experimental 

 breeding. Much has been written and many conjectures 

 made by earlier horticulturists in their attempt to classify 

 hybrids so that inheritance could be found to proceed in 

 an orderly and regular manner. All of these attempts 

 had been more or less failures until Gregor Mendel, an 

 Austrian monk, began a series of classic experiments in 



