LINDSTROM, GENETICAL RESEARCH WITH MAIZE 331 
The reason for these two distinct types of ears seems to lie in the na- 
ture of the pistillate flower. The normal ear of corn consists of a series 
of paired spikelets borne along the full length of the cob. Each spikelet 
holds two flowers. In the ears with a regular, paired distribution of 
grains, only one flower in each spikelet develops. The other aborts. The 
irregular distribution is thoughttooccurbythedevelopmentand growth 
of both flowers in the spikelet. This causes a pronounced crowding of 
the grainswhich destroys the regularity of the ear.Such ears are charac- 
terized by long, slender grains tightly wedged against one another. 
Despite considerable variation, commercial varieties of corn exhibit 
a typical number of rows. The larger dent varieties average 16 to 18 
rows with a range from 8 to 28 rows.The flint corns are characteristical- 
ly 8- or 12- rowed with less variability. Among the sweet corn varieties 
there are 8-, 12- and 16- rowed modal types. The greater variability is 
shown by varieties with the larger number of rows. 
The inheritance of row number is not satisfactorily solved in detail. 
The experiments on crossing varieties with different numbers of rows 
have shown that in general the inheritance is analogous to that of 
other quantitative characters. (Emerson and East 1913). 
Endosperm Characters. 
Maize is rich in endosperm characters. Not only do the different tis- 
sues of the endosperm exhibit various colors, but they show also mar- 
ked types of physical texture of the endosperm. The inheritance of 
such characters has been placed on a stable basis, one that both corres- 
ponds to and verifies the cytological mechanism that produces the en- 
dosperm tissue. The phenomemon of xenia is very common in maize. 
The endosperm of maize is a peculiar structure. It is neither gameto- 
phytic nor sporophytic tissue. It is the result of a triple fusion of nuclei 
in the embryo sac, two nuclei from the female gametophyte and one 
from the male gametophyte. From the chromosome standpoint it is in 
the 3n condition. This situation provides a splendid opportunity for 
determining whether or not two doses of a factor (from the female) may 
overbalance one dose of the male. Evidence on this is presented later. 
In order to understand and appreciate the genetics of endosperm 
characters in maize the structure of a corn grain must be familiar. The 
following diagram is intended for that purpose. 
