572 THE AMERICAN- NATURALIST... (VoL; XXXIX, 
B V 
^ 
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 òf 
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 phasg 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 ‘ewe 
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 ori 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 cogcern 
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 Brünn, Austria, under the dates 1865 
and 1869. They lay buried until 1900 when De Wes, Cogrens, 
and Tschermak independently rediscovered themgand 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 
