which are isolated at opposite sides and opposite ends of 
an internode. Our grouping is more convenient for floral 
comparisons, especially when the internodes are tele- 
scoped: the axillary buds are either closely associated 
with or fused to their subtending leaf or leaf rudiment, 
and the lateral organs are whorled, as in the maize ear. 
Repetition of the phytomer. Control over the number 
of repetitions of the phytomer, as well as their individual 
manifestation, usually seems to follow a functional pat- 
tern which is characteristic for a certain portion of the 
plant. In the lower parts of the plant, all organs of the 
phytomer are large, photosynthetic structures (Plate I, 
A), while in the highly compacted inflorescences, their 
counterparts may be reduced or entirely obliterated 
(Plate I, B through F). 
The typical course of repetition by the phytomer in 
a given area of the maize plant may be changed by un- 
usual genetic and/or environmental conditions. In short- 
day maize, as in other photoperiodic plants, the number 
of repetitions by vegetative-type phytomers and the time 
of change to a floral-type of manifestation is controlled 
by length of day. Also the production of vegetative phy- 
tomers by axillary buds, as well as the abruptness of their 
ultimate shift to a floral manifestation, seem to be con- 
trolled by the corn-grass (Cg gene) locus. At least four 
other genes contro] the production of phytomers at spe- 
cific points in the inflorescence, as follows: 
The primary branches (rachids), ramosa 1, 2 (ra1, ae) 
on chromosomes 7 and 8; 
The spikelets, branched-silkless (bd) on chromosome 
ic: 
The florets, polytypic (Pt) on chromosome 6. 
Gross STRUCTURE AND MANIFESTATION 
OF THE PHYTOMER 
Evidence of homologous relationships based on gross 
[ 5 ] 
