Variation and Correlation of Oats — Part II 83 



In addition to the study of the correlations as they exist in oats, other 

 features liave been introduced in order to determine the status of corre- 

 lation studies, to find out how correlations may be modified, and to 

 determine which correlations are capable of modification. These studies 

 have gone hand in hand with studies of the mean and of variation. 



The method used in determining the correlation coefficients herein 

 reported is the short method given by Rietz and Smith (1910). The 

 correlation tables and frequency distributions were made from the data 

 taken on the plants, which had been copied on cards, one card containing 

 all data for the culm or the plant dealt with. The cards for any series 

 were then grouped according to the classes of the subject character, and 

 each group was then divided according to the classes of the relative char- 

 acter. By counting the cards in the final groups and entering the num- 

 bers in the proper rectangle, correlation tables were made. All formulae 

 used are contained in Davenport's " Principles of Breeding " (1907). 



CHARACTERS USED 



The characters of oats dealt with in these studies are; 

 Height of culm and average height of plant 



The height of culm was measured, in millimeters, from the root crown 

 to the base of the apical spikelet. The average height of plant was 

 determined by dividing the sum of the culm lengths by the number of 

 culms possessed by the plant. 



Average length of head per plant 



This was obtained by dividing the sum of the head lengths of the plant 

 by the number of culms per plant. The length of head was measured, 

 in millimeters, for each culm, the head being considered as extending 

 from the node marking its origin to the base of the apical spikelet. 



Weight of plant 



Total weight of plant. — This was obtained usually by weighing the 

 entire plant, exclusive of the root, in centigrams. In some cases it was 

 obtained by adding together the weights of the separate culms of the plant. 



Total weight of culm. — This was obtained for a few series by weighing 

 in centigrams, separately, the different culms making up the plant, using 

 the entire culm, exclusive of the root. This is the same as the total 

 weight of plant in cases of single-culmed plants. 



