Lindstrom: Chlorophyll Factors of Maize 
Among a total of 1338 grains in 
Table IV, 365 or 27.3% are of the 
abortive type. Presumably, then, we 
are dealing with a recessive, Mendelian 
factor that inhibits the formation of 
both embryo and endosperm. 
The abortive grains occurred in a 
family of plants that were showing seg- 
regation into green and chlorophyll-free 
seedlings. It is to be expected that 
when the green plants of such a family 
are self-fertilized, a certain proportion 
of them will segregate in the next gen- 
eration. Only four green plants (2208 
(1), (2), (4), (7) ) were self-pollinated 
and they produced nothing but pure 
green progenies. Four is too small a 
number on which to base conclusions, 
but it does suggest the possibility of 
some relation between the abortive 
grains and the seedlings deficient in 
chlorophyll. 
This relation might be conceived of 
as a case of complete linkage between 
a lethal factor destroying both em- 
bryo and endosperm and another 
lethal factor inhibiting the formation 
of normal chlorophyll. Since the orig- 
inal F, generation was segregating 
for both the white and virescent-white 
seedling factors, it is impossible to 
judge which of the two might be con- 
cerned in such a linkage. Further 
tests are being planned to determine 
this. 
There is also a possibility that we 
are not dealing with a case of linkage at 
all, but that the abortive grains are 
due to some physiological interrelation 
of the chlorophyll factors. Since, how- 
ever, all the known chlorophyll ab- 
normalities have been tested against 
each other and have reacted and seg- 
regated as ordinary Mendelian factors, 
it does not seem re sonable to suppose 
that they would, in themselves, have 
any such radical effect as to destroy 
both embryo and endosperm. 
The relation between the abortive- 
grain character and inbreeding is 
similar to that of the other recessive 
277 
1a; 
characters mentioned in the first para- 
graph of this article. If present in a 
strain of maize, although they might 
be unsuspected, being hidden by the 
dominant, normal allelomorph, these 
abortive grains would begin to appear 
when the strain was inbred. This 
would decrease the yield of such a 
strain seriously. The abortive-grains 
could be eliminated, with some diffi- 
culty however, but if any favorable 
characters were closely linked with 
them, they too would be eliminated. 
SUMMARY 
Certain striking chlorophyll abnor- 
malities are shown by breeding evi- 
dence to be distributed in several 
different chromosomes of maize. From 
this it is to be inferred that other less 
pronounced deficiencies of chlorophyll 
are distributed in a similar manner. 
The latter especially are common in 
commercial fields of corn and presum- 
ably are responsible for decreasing or 
limiting the productivity of the plant 
to some extent. They would naturally 
be isolated and removed in an intensive 
system of selective inbreeding, since 
they are recessive in nature. Being 
distributed on different chromosomes 
their elimination would tend also to 
remove some of the more favorable 
factors which, being on the same 
chromosomes, would naturally follow 
the defective factors in inheritance. 
In this manner, it is very likely that 
continuous inbreeding removes favor- 
able as well as unfavorable factors 
from the original stock. 
To succeed in a system of maize in- 
breeding then, it is essential to begin 
with the best source of material avail- 
able, a source that is as free of abnor- 
malities and defects as possible. It 
is probable that inbreeding of such 
stock might be carried out with very 
little loss of stature, yield or fertility 
and would at the same time improve 
the uniformity of the type. 
