THE ANCESTOR OF CORN—-MANGELSDORF 505 
develop in three different environments. The first plant, a short, 
single-stalked plant with a slender, unbranched tassel bearing both 
male and female flowers and no ears, is intended to represent the wild 
corn plant growing in nature in a site of low fertility and in severe 
competition with other natural vegetation. Such a plant would barely 
reproduce itself. 
The second plant represents this same genotype grown under primi- 
tive agricultural conditions. Here it is still single-stalked but under 
these somewhat better conditions is capable of producing a branched 
tassel and a single small ear borne high upon the stalk. The third 
plant (a counterpart of the third plant in pl. 3, fig. 1) represents the 
genetically reconstructed ancestral form grown under modern agri- 
cultural conditions with an abundance of fertilizer and in freedom 
from competition with weeds. Under these conditions it has several 
stalks as well as several small ears on each stalk. Plants like these 
might also have occurred sporadically in the wild under unusually 
favorable natural conditions, 
The ability of the wild corn plant to respond in a spectacular 
fashion to freedom from competition with weeds and to high levels 
of fertility is undoubtedly one factor which led to its domestication. 
This ability to take full advantage of the improved environment 
usually afforded by an agricultural system is one of the characteristics 
found in almost all highly successful domesticated species. There are 
many wild species which do not have this trait; they cannot stand 
prosperity. 
Since the corn plant is genetically plastic as well as responsive to 
an improved environment, domestication may soon have brought other 
changes, which are illustrated in the last four plants in figure 4. 
One of the most important of these was a mutation at the pod-corn 
locus on the fourth chromosome. This single genetic change had 
numerous effects. It reduced the glumes which in wild corn com- 
pletely surrounded the kernels, and the energy released from chaff 
production now went into the development of a larger cob, which 
in turn bore more and larger kernels. The mutation also lowered 
the position of the lateral inflorescences, and this had profound effects 
of several kinds which can be understood by referring again to figure 
3. This shows that: (1) The lower the ear, the stronger the stalk at 
the position at which the ear is borne and the greater its capacity for 
supporting large ears. (2) The lower the ear, the more likely it is 
to bear only female flowers which develop kernels when pollinated. 
(3) The lower the ear, the longer the shank, the branch on which 
it is borne, and this in turn has a number of important secondary 
effects: the longer the shank, the more numerous its nodes or joints 
and the husks which arise from them; the greater the number of 
