XIV Journal of Agricultural Research vol. xx 



69. A. — Mannite-nitrate agar slants, 8 days old, from left to right: soybean 



bacteria, vetch bacteria, and Bacillus radiobacter. B. — Growth in milk, 



4 weeks old, from left to right: soybean bacteria, vetch bacteria, and 



B. radiobacter. C. — Growth on potato, 2 weeks old: vetch bacteria (left) Page 



and B. radiobacter (right) 556 



Correlation and Causation 

 Text Figures 



1. Diagram illustrating the interrelations among the factors which determine 



the weight of guinea pigs at birth and at weaning (33 days) 560 



a. Diagram showing relations between two variables, X and Y, whose values 

 are determined in part by common causes, B, C, and D, which are in- 

 dependent of each other 565 



3. Diagram showing relations between two variables, X and Y, whose values 



are completely determined by common causes, B and C, which are in- 

 dependent of each other 565 



4. A system in which the value of variable X is completely determined by 



causes M and N, which are correlated with each other 566 



5. A system in which the value of X is affected by a factor, B, along two differ- 



ent paths, BMX and BNX 567 



6. Diagram showing relations between two variables, X and Y, whose values 



are determined in part by common causes, M and N, which are correlated 



with each other 568 



7. Simplified diagram of factors which determine birth weight in guinea pigs. 568 



8. Path coefficients measuring the relations between birth rate (X), rate of 



growth (Q), gestation period (P), size of litter (L), and other causes (A, 



C) 570 



9. Coefficients of determination. Symbols as in figure 7 570 



10. Effect and one known cause 571 



11. Effect and two correlated known causes 571 



12 . Effect and three correlated known causes 571 



13. Effect and four correlated known causes 572 



14. Relations between wet-bulb depression (B), wind velocity (W), radia- 



tion (R), and temperature (T) as assumed for direct analysis 576 



15. Relations between factors of figure 14 and absolute humidity (H) expressing 



causal relations better than figure 14 but adapted only to indirect analysis. 579 



16. Relations between evaporations or transpiration (X) and the system shown 



in figure 15 582 



Inheritance op Syndactylism, Black, and Dilution in Swine 



Plate 



70. The four types of F 2 segregates from a cross between mule-foot boar and 



Duroc- Jersey sows. A. — Black mule-foot. B. — Black cloven foot. 



C. — Red mule-foot. D. — Red cloven foot 604 



Four Rhynchophora Attacking Corn in Storage 

 Plates 



71. Araecerus fasciculatus . A. — Pupa, dorsal view. B. — Pupa, front view. 



C. — Egg. D. — Mandible. E. — Mature larva. F. — Ventral view of head. 

 G. — Labium and clypeus. H. — Pupa, lateral view. I. — Head, face view. 

 J. — Head, dorsal view. K. — Head, lateral view 614 



