| Antecedents | Consequents |
| A L M T | p q r g |
| B L M E | z q r x |
| B C M E | r z x y |
| A M T H | p q g o |
(18) “Mr. Darwin, in his experiment on cross and self fertilization in the vegetable kingdom, placed a net about one hundred flower heads, thus protecting them from the bees. He at the same time placed one hundred other flower heads of the same variety of plant where they would be exposed to the bees. He obtained the following result: The protected flowers failed to yield a single seed. The others yielded about 2,720 seeds. Thus cross-fertilization was proved.” (Hibben).
What method did Darwin employ? Symbolize the experiment.
(19) Summarize the distinguishing marks of the joint method.
(20) Show that the joint method is more ideal than either agreement or difference.
(21) State and give concrete illustrations of the law of concomitant variations.
(22) What is the chief function of concomitant variations? Illustrate.
(23) Give instances where it would be impossible to use difference, but easy to use concomitant variations.
(24) Explain this: “The quantitative variation between antecedent and consequent may be either direct or inverse.”
(25) State and explain by illustration the method of residues.