766 
tion of these facts. Just at present we 
have more facts of a certain kind than we 
know what to do with. We need some one 
to put meaning into these facts. We are 
in the position of a man lost in a wilder- 
ness. What he needs to find is a road. 
It does not make so much difference where 
this road shall lead, for all roads lead into 
each other. If he can find any road, it 
will lead him to where he can find people, 
and these can point out other roads leading 
more nearly in the direction he wants to go. 
In genetic investigations we need the- 
ories that will suggest lines of investiga- 
tion that will be fruitful of results—that 
will lead, not to more facts of the kind we 
already have, but to new kinds of facts 
that will throw light on the subject from 
a new angle. ‘‘Theories,’’ said Pasteur, 
“come into our laboratory by the bushel. 
When they have served their purpose, they 
are thrown out of the window.’’ This has 
been so in the development of the science 
of genetics, but just at present the supply 
of theories is almost exhausted. 
The things that need interpretation are 
the manner in which segregation and re- 
combination are brought about, the nature 
of the things that segregate and recombine, 
~ and their relation to the processes of deyel- 
opment. Mendelian factors, that is, those 
factors of development that behave in Men- 
delian fashion in heredity, of necessity re- 
late only to those differences that exist 
between organisms that are closely enough 
Yelated to cross-breed with the production 
of fertile progeny. In certain species 
crosses, and in some other cases in which 
there is reason to suspect either a diseased 
condition of the cytoplasm, or a departure 
from the normal behavior in gametogenesis, 
cases have been found in which the factors 
of development do not segregate and re- 
combine in the simple manner represented 
by the Mendelian formule. Aside from 
SCIENCE 
[N.S. Vou. XXXV. No. 907 
these cases, it seems a fair inference from 
the results thus far obtained that the dif- 
ferences between organisms sufficiently re- 
lated to permit of cross-breeding with the 
production of fertile offspring which re- 
produce sexually in a normal manner, are 
universally subject to the laws of segrega- 
tion and recombination. There is one 
quasi-exception to this statement; there are 
certain factors that, instead of segregating 
im the usual presence-absence fashion, seg- 
regate from each other, so that they can not 
reside permanently in the same pure-breed- 
ing line. In my cowpea investigations I 
have found a set of three such factors; 
when only one of these is concerned in a 
cross we get the usual phenomena of pres- 
ence-absence segregation. But if any two 
of the three are brought together in the 
same zygote they segregate from each other. 
These three factors are the factor Br, above 
mentioned (the special factor for brown 
pigment in the seed coat), and the New 
Era and Taylor types of speckling. 
The question whether the deeper and 
more fundamental characters of the organ- 
ism, such as are concerned in the differ- 
ences between organisms widely separated 
in the organic world, are inherited in Men- 
delian fashion is purely academic and of no 
practical importance either to the theory 
of heredity or the practise of the breeder, 
for this question can never be submitted 
to experiment, nor could the most definite 
knowledge on this point be applied in the 
production of new and improved races of 
plants and animals. 
At present Mendelists are plodding along 
practically without working theories. Let 
us hope that some of them will stumble on 
to facts of a new kind that will give mean- 
ing to those we already have. 
Personally, I am of opinion that the 
chemistry of the pigments is a field that 
is of great importance to the theory of 
