THE HEREDITARY BASIS 17 
trasted characters. What is now known of the germ cells enables 
us to point with great probability to the cellular mechanism by 
which this purity of the gametes or mature germ cells is main- 
tained. The same mechanism also affords an explanation of the 
phenomenon of linkage or the tendency of diverse characters to 
maintain a certain association in inheritance. The mechanism 
consists of the chromosomes of the nucleus which there are strong 
reasons for believing maintain their individuality, as they do their 
number, not only through numerous cell generations in the life of 
the individual, but through an indefinite number of life cycles of 
individual organisms. The behavior of these chromosomes in 
maturation and the process of synapsis immediately preceding 
maturation is precisely such as would explain the distribution of 
characters according to Mendel’s law if we grant that individual 
chromosomes contain factors for the production of particular 
characters. We cannot give an idea of the remarkable success 
that has been attained in connecting the phenomena of inheri- 
tance with peculiarities of chromosome behavior, and must refer 
the reader to special works and papers dealing with this topic. I 
can scarcely do more than indicate in a short chapter the various 
applications of Mendel’s law in interpreting many enigmatical 
phenomena of inheritance. The phenomena of reversion, the 
results of inbreeding, the heredity of sex and the peculiar phe- 
nomena of sex-linked inheritance are seen in a new light since 
the discovery of Mendel’s law. 
Since Mendel’s law has been found so widely applicable in 
plants and animals, we should expect to find it expressed also in 
the inheritance of man. Already numerous human traits are 
known which give strong evidence of being transmitted in accord- 
ance with thislaw. Since it is not feasible to treat human beings 
as we do plants and animals it is difficult to ascertain in many 
cases whether inheritance is in fact strictly Mendelian. A list, 
though incomplete, of traits which are probably transmitted 
according to Mendel’s law is given in the following table: 
