vestigial glume condition demonstrates a potential in 
maize to evolve a Tripsacoid-type of glume. 
The evolutionary changes resulting in shorter glumes 
during the domestication of maize could hardly have in- 
volved mutation at the ’g—vg locus. The Vg gene is a 
rare type of dominant mutation which seems to be of 
recent origin. Furthermore, it is not known to be part 
of a multiple-allelic series such as has been reported for 
the Tu-tu locus. There is also strong morphological evi- 
dence that the Vg gene has not been active in maize 
evolution. If such V’g activity had occurred, then it 
would be revealed by a characteristic reduction of the 
lateral wings of glumes. On the contrary, these wings 
are well-developed and papery in both modern and 
archaeological maize. In teosinte and Tripsacum, how- 
ever, the glume wings are somewhat reduced and highly 
lignified. 
In the series Tu; normal; Vg, decreases in glume- 
length are accompanied by increases in the thickness of 
the outer lignified zone. Since lignification of this outer 
zone of the glume occurs at the same time as kernel- 
development, there may be competition for the available 
energy. In the tunicate series of alleles (Mangelsdorf and 
Mangelsdorf, 1957) some of the energy conserved from 
shorter glumes is apparently diverted to increased grain 
production in spite of an increase in glume-lignification. 
Experiments are now in progress to determine the effect 
of the Vg gene on yield of mature grain. 
Pn glumes exemplify a condition which does not fit 
into this pattern of variation and, notwithstanding the 
suggestion of Andrés (1950), could scarcely have exer- 
cised a protective role at any stage in the evolution of 
maize. The only possible evolutionary counterpart of 
papyrescent glumes in other grasses appears to be repre- 
sented by a certain degenerate change found in several 
[73 | 
