spikelets of T'ripsacum are subjected to increased lateral 
compression from tightly binding husks of maize, the 
spikelets then become more deeply embedded in the 
rachis, and various reductions in the pith, vascular sys- 
tem and cell size follow. 
It is curious that the vascularization associated with 
all three of the rudiments studied—the glume cushion, 
the pulvinus and the cupules or hollowed rachis seg- 
ments—appears to be a part of the rind of the rachis, 
rather than to represent vascular vestiges of their appar- 
ent homologues. But the tissues of these rudiments, as 
well as the effects of unusual genetic or environmental 
conditions, reveal their homology to organs which cor- 
respond to that of their apparent phytomeric position. 
In the ultimate axes or rachillas, the parts of the phy- 
tomer become obvious. The first two phytomers of the 
rachilla have reduced axillary buds and produce little 
more than the leaves or glumes. But, in more distal 
phytomers, the leaves (now called lemmas) subtend a 
bud of sexual organs and its associated prophyll or so- 
called ‘‘palea.”’ 
The gross structure of the entire plant in maize and 
its relatives is organized upon a basic pattern of organs, 
the phytomer. The variations in expression which the 
phytomer has sought in different portions of the plant 
may (as Arber has suggested with respect to orders) be 
compared with the intrinsic beauty of a ‘‘theme with 
variations’ as expressed in certain musical compositions. 
Both represent harmonious variations upon a repetitious 
design, and both obey the dictates of an overall plan. 
ACKNOWLEDGMENT 
During the course of the investigation and preparation 
of the manuscript, many helpful suggestions were made 
by Professor Paul C. Mangelsdorfof Harvard University. 
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