THE ANCESTOR OF CORN—MANGELSDORF 501 
By combining these modifying and inhibiting genes from several 
popcorn varieties with the pod-corn gene, we have developed a number 
of strains of popcorn which, having this gene present on both of their 
fourth chromosomes, breed true for the pod-corn character. Some of 
these homozygous strains are much less monstrous than the usual 
forms of pod corn, are completely fertile, and might under suitable 
conditions be capable of surviving in the wild. 
EFFECTS OF A SINGLE GENE 
The majority of these true-breeding pod-popcorns have other char- 
acteristics which we may now regard as primitive. The plants, when 
grown on fertile soils, instead of having one stalk, as do most modern 
corns, have several (pl. 3, fig. 1), and in this respect resemble the 
majority of wild grasses, including all the known relatives of corn, 
both American and Asiatic. The plants are shorter than ordinary 
corn because one of the numerous effects of the pod-corn gene is to 
shorten and thicken the upper internodes of the stalk. This is well 
illustrated in plate 3, figure 1, which shows three plants of popcorn 
in one family: one lacking the pod-corn gene, one having the gene on 
one member of its fourth chromosome pair, and one having the gene 
on both members of the pair. There is a progressive decrease in 
height through this series of three genotypes resulting from a short- 
ening of the upper internodes. This shortening causes, or at least is 
accompanied by, the development of a terminal inflorescence which 
bears both male and female flowers, the male flowers at the tips and 
the female flowers at the bases of the same tassel branches (pk 2). 
These branches are quite brittle when mature and break apart easily 
when disturbed by the wind or by birds. They thus provide one 
of the most important primitive characteristics which cultivated 
corn lacks: a mechanism for the dispersal of seeds. 
POSITION OF THE EAR 
Plants of homozygous pod corn frequently do not have ears—most 
of their energy is apparently concentrated in the terminal] in- 
florescences—but when they do have ears these are usually borne high 
upon the stalk (pl. 2), often at the joint of the stem immediately 
below the tassel. This elevation of the position of the ear has pro- 
found effects which are illustrated by the diagram in figure 3. The 
diagram, which is based on data from several many-eared plants, 
shows how a number of the characteristics of the ears are determined 
by their position on the stalk: (1) The higher the position, the 
smaller the ear, partly for the simple mechanical reason that the stalk 
at this position is slender and is incapable of bearing a heavy load. 
It would be mechanically impossible for the large modern ear of corn 
