910 
mental problems of cell behavior and 
heredity. 
The relative share in this stimulus to re- 
newed and hopeful study of the facts 
which is to be assigned to the older theories 
of the germ plasm and to the new observa- 
tions of mutation, dominance, segregation, 
synapsis, ete., is a question which may be 
left to the historian of biological science 
in the future to determine. There can be 
no question that De Vries’s theory of pan- 
genesis has guided in large degree his ex- 
perimental studies in mutation. 
Tt will certainly be of interest to attempt 
to discover how the new observations are 
related to the older theories of the germ 
plasm and especially to try to learn how 
the numerous experimenters and breeders 
who are putting forth such a flood of data 
on hybridization, pure-line breeding, bud 
variation, graft hybrids, ete., find it neces- 
sary to modify or discard and replace the 
terms and conceptions of the older theories 
in order to give an intelligible account of 
their observations. 
The theories of Naegeli, Darwin, Weis- 
mann and De Vries ean all be characterized 
as Detto and others have made clear, as cor- 
puscular theories of heredity and organi- 
zation more or less frankly based on an 
assumed analogy between the ultimate 
constitution of matter as given in the 
atomie theory and the grosser mechanical 
organization of living plants and animals. 
The fate of this assumption in the hands 
of experimental breeders and students of 
the cell is certainly a matter of great in- 
terest. 
We may first note that the outcome of 
all this activity of research, both in eytol- 
ogy and breeding, has made it inereas- 
ingly certain that we do have in the perma- 
nent structural constituents of the nucleus 
a real physical basis of heredity. The evi- 
dence available ten years and more ago, 
SCIENCE 
[N.S. Vou. XXXV. No. 911 
that the chromosomes transmit the hered- 
itary characters of the adult organism in 
so far as they are directly transmitted, 
which is based on the permanence of the 
chromosomes through successive genera- 
tions, due to their method of reproduction 
by equational division, their constancy in 
size, number, shape and position in the 
germ cells, however the latter may differ in 
shape, motility, cytoplasmic mass, ete., has 
been continually strengthened as the re- 
sult of a more careful analysis and inter- 
pretation of results. 
The attack on the specific character of 
the chromosomes and their reproduction 
by splitting, which has been made in the 
contention repeatedly appearing from 
both botanists and zoologists, that nuclei 
may divide by so-called direct division, 
that is, simple constriction, and still con- 
tinue capable of perpetuating the species, 
has in every case on more careful study 
been found to be due to faulty interpreta- 
tion or inadequate methods of observation. 
Only a passing reference to the exploded 
notions of Pfeffer as to Spirogyra and 
Child as to certain flat worms is necessary 
in this connection. Cases of apparent 
preponderance of the female, such as the 
echinoderm hybrids, in which the enucle- 
ated egg cytoplasm determines the type of 
cleavage and early embryonic development, 
are always those in which the egg has be- 
come a highly specialized cell by reason of 
the accumulation of yolk stuffs, ete. That 
a cell so enlarged should have also devel- 
oped what has been called a promorphol- 
ogy is natural enough. That this precon- 
jugation organization is that of the species 
to which the egg belongs is inevitable, but 
such cases can have no final significance in 
determining the question of the relative 
functions of nucleus and cytoplasm in he- 
redity. Perhaps the best recent evidence 
that elements of the cytoplasm may also 
