THE IMPORTANCE OF BROAD BREEDING IN CORN. 4] 
THE ELIMINATION OF “BARREN STALKS.”’ 
Another factor which has worked toward the inbreeding and con- 
sequent deterioration of highly bred varieties of corn is the removal 
of the so-called “ barren stalks.” The elimination of nonproductive 
plants is undoubtedly desirable, but the removal of barren stalks as 
usually practiced is not a step in this direction. A truly barren stalk 
is one that fails to produce seed. So far as the seed is concerned, 
therefore, this elimination is automatic and inevitable, but it has been 
urged that the barren stalks must be removed before they produce 
pollen, on the theory that pollen from barren stalks is likely to cause 
deterioration in the progeny of neighboring plants. Where this 
practice is followed it results only in the detasseling of all proteran- 
drous plants, for, as pointed out by Soule and Vanatter,’ it is impos- 
sible to distinguish the truly barren plants at the time of tasseling. 
With many‘ wvarieties, especially those which have not been subjected 
to rigid selection, some of the plants which eventually prove to be 
the most prolific show only small rudiments of ears at the time of 
tasseling. The continued removal of such plants results not in the 
elimination of barren stalks, but in the elimination of the plants 
which possess a valuable adaptation to avoid self-pollination. This 
weeding out of the more proterandrous individuals has been continued 
with some varieties until the majority of the plants produce staminate 
and pistillate flowers at the same time. When these varieties flower 
in comparatively still weather, there must be a large proportion of 
self-pollinated seed and a consequent weakening of the variety. This 
persistent tendency to proterandry can be thought of as a natural 
reaction of the species against the danger of extinction from inbreed- 
ing. Even the true barren stalks might represent a tendency on the 
part of the plant to become dicecious. In localities with very short 
seasons it may be well, to discriminate against the tendency in the 
plant to put out ears too long after the tassel has matured, but 
elsewhere the avoidance of self-pollination is more important. 
CONTINUOUS IMPROVEMENT THROUGH SELECTION. 
The fact that narrow breeding in corn results in a reduction of 
vigor has remained unappreciated largely because narrow breeding 
is always accompanied by selection for yield and vigor. The two 
processes are opposed, so that movement in either direction is masked 
and counteracted. Varieties thus produced are delicately adapted 
to the exact conditions under which they have been selected, and often 
show marked deterioration when placed under new conditions. The 
very delicacy of the adjustment helps to insure the much desired 
. 2 Bulletin 165, Virginia Agricultural Experiment Station. 
141—I1y 
