476 THE AMERICAN NATURALIST. . (VoL. XXXIX. 
interesting subjects of cell research. Reduction phenomena also 
have a deep phylogenetic significance whose history in plants at 
least can be traced with a remarkable degree of exactness. 
We are confident that sporogenesis in plants signifies the sud- 
den return of the organism to the condition of an ancestral 
sexual generation with the reappearance of a primitive number 
of chromosomes. The short time consumed in the process and 
the details and precision of the cell activities show that we are 
dealing with phenomena whose complicated mechanism can only 
find explanation in a long phylogenetic history. In the study of 
reduction phenomena and fertilization we have reached the con- 
clusion that the chromosomes are intimately concerned with the 
transfer of hereditary qualities and are probably the chief or 
even the sole bearers of these characters. And thus we enter 
upon some of the most far reaching problems of biology, those 
of heredity, hybridization, and the basis for the remarkable 
ratios of inherited characters which Mendel first clearly set 
forth. 
It seems quite certain for both animals and plants that numer- 
ical reduction of the chromosomes takes place through an asso- 
ciation of the paternal and maternal chromosomes in pairs to 
torm the reduced number of bivalent chromosomes (dyads). We 
have presented in Section IV (Sexual Cell Unions and Nuclear | 
Fusions ") the evidence which indicates that paternal and maternal 
chromosomes do not unite at the immediate time of nuclear 
fusion in fertilization. On the contrary, in all higher animals 
and plants the paternal and maternal chromosomes are believed 
to remain separate throughout the long series of cell divisions in 
the new generation up to the time of ‘sporogenesis in plants and 
gametogenesis in animals, both events being characterized by 
reduction phenomena. The fusion of the chromosomes takes 
place in the growth period which differentiates the spore mother- 
cell in plants from the archesporium or the primary gametocyte 
in animals from.the preceding gametogenous tissue. The growth 
period is one of general protoplasmic accumulation and increase 
in the chromatin content of the nucleus, and is especially char- 
acterized by that peculiar activity in the nucleus termed synap- 
sis. Evidence is accumulating that synapsis is the characteristic 
