572 THE AMERICAN NATURALIST. [Vol. XXXIX. 



7. Hybridization. 



This is not to be a detailed discussion of the facts and theories 

 of hybridization, a subject far too extensive for the purposes of 

 our treatment. We shall only consider some of the bearings of 

 the recent studies on fertilization and reduction phenomena upon 

 the problems of hybridization treating it as a critical phase in 

 the life history of the organisms concerned. Until recently the 

 attempts to formulate definite laws for the formation of hybrids 

 and their progeny upon a physical basis have not been satisfac- 

 tory. But the work of a number of breeders all of whom owe 

 their results in large part to a quick appreciation of Mendel's 

 epoch-making contributions have brought much order out of 

 what was a very confused subject. And accompanying the 

 work of this group must be added the equally important con- 

 clusions of a number of cytologists whose investigations on the 

 structure and behavior of nuclei in the critical periods of fertil- 

 ization and chromosome reduction have done much to place 

 Mendelian principles upon a cytological basis. We shall deal 

 with the work of the latter group, for their contributions concern 

 intimately the subject matter of these papers. 



We shall not review the conclusions of Mendel except to point 

 out the relations of some of his principles to cytological phenom- 

 ena. The two papers of Mendel appeared in the proceedings of 

 a natural history society of Briinn, Austria, under the dates 1865 

 and 1869. They lay buried until 1900 when De Vries, Correns, 

 and Tschermak independently rediscovered them and called the 

 attention of the scientific world to their worth. Soon after, 

 Bateson published a translation of the two papers {Mendel's 

 Principles of Heredity, Cambridge, 1902) with an introduction 

 and a defense against the criticisms of Professor Wheldon. There 

 have naturally been many reviews and short discussions of Men- 

 delian theories and among them that of Castle entitled " Mendel's 

 Laws of Heredity" {Science, vol. 18, p. 396, 1903) and Profes- 

 sor Bailey's "Lecture IV" in Plant Breeding, 1904, will per- 

 haps give the reader the clearest and most concise statements. 



The most striking feature of Mendel's investigations and those 



