118 PROCEEDINGS OF THE OHIO ACADEMY OF SCIENCE 



extraordinary field for expetimental work. This has 

 already developed to vast proportions in connection with 

 both the results obtained and the speculations involved, 

 while the end is not in sight. 



The investigations of Mendel, now so familiar to all 

 biologists, and which may be mentioned somewhat in detail 

 here because of their bearing on mutation, consisted prima- 

 rily in the crossing of tall and dwarf peas with the result 

 that the first filial (FJ or hybrid generation consisted 

 entirely of tall plants. When, however, seed from these 

 plants was sown the ratio of tall to dwarf plants became 3 

 to 1 in the second (F.) hybrid generation, a result explained 

 by the theory of dominant and recessive characters on the 

 basis that there are certain determiners of unit characters 

 in the germplasm dominating over others during the 

 development of the somatoplasm or body of the individual 

 in the higher forms of life. More recently the presence and 

 absence theory has been applied in interpreting the results. 

 In a manner similar to the preceding, when smooth, yellow 

 peas were crossed with wrinkled green peas, the first hybrid 

 generation consisted of smooth yellow forms inasmuch as 

 the character smooth and the character yellow were domi- 

 nant over the character wrinkled and the character green, 

 and the crosses were known as dihybrids inasmuch as they 

 differed in respect to two characters. In the second hybrid 

 generation the resultant ratio was 15 to 1 pure recessive, 

 i. e., wrinkled green although the fifteen consisted of smooth 

 yellow, smooth green, and wrinkled yellow in the proportion 

 of 9 :3 :3. In the same way trihybrids have the ratio 63 to 1 

 pure recessive while and polyhybrid differing in "n" char- 

 acters, which mendelize in the usual manner, will give an 

 expected ratio of 4"-l to 1 pure recessive and only become 

 apparent through the breeding of large numbers of indi- 

 viduals. 



While the preceding summary represents the normal 

 results in connection with the segregation of unit charac- 

 ters, studies of the past few years have demonstrated that 



