HEREDITY, AND THE ORIGIN OF SPECIES. 9 
plex case in which the partial fusion of unequal chromo- 
somes, with divisions of the chromosomes may operate 
in a manner to secure anything but purity of the germ-cells. 
The results of such complicated integrations and split- 
tings are incidental to the scope of this lecture however, 
as we are concerned at present only in those cases in which 
fixed forms result from hybridization, chiefly in the first 
generation. So far have we advanced, however, in the 
study of the behavior of hybrids, that with the information 
obtained from them, and with the recent discoveries as to 
the differences of chromosomes, we may well believe that 
we are now at the dawn of a new day in the study of hered- 
ity and all of its associated problems, in which the greater 
results are to come from the proper and closer correlation 
of the researches of workers in all branches of natural 
science. 
The second method by which new characters and new 
species have been seen to arise in the succession of genera- 
tions’in plants is that of discontinuous variation, or muta- 
tion. In following out the germination of hundreds of 
seeds in pedigreed strains of plants, a few individuals may 
be found in each generation, which are notably different 
from the type in anatomical and physiological features. 
These divergencies are variously heritable, constituting 
breaks in descent, by which, in some cases, new species 
originate. Such seed-sports or seed-mutants have been 
seen hundreds, perhaps thousands of times during the last 
two centuries, but it is only within the last twenty years, 
that their phylogenetic importance began to be appreciated. 
It will be of interest to this assembly to know that Ameri- 
can botanists and horticulturists have made early observa- 
tions of direct interest in this connection. Thus Dr. Arthur 
Hollick, while a student at Columbia University in 1879, 
said in writing of white varieties of colored plants: “First 
then, we have to consider those sports of nature where 
