time the plant is only a few weeks old and it continues 
throughout the development and maturation of the ear. 
Its role in cupule formation in maize and its relatives 
seems obvious. Here, in the position of maximum com- 
pression between two axes, the central portion of the 
rudimentary prophyll and associated rachis tissue seems 
to be depressed inward by penetration of the expanding 
spikelets. The resulting stresses have apparently inhib- 
ited development of the small rind bundles, while the 
larger bundles deeper within the rachis buckle under 
stress and bend inward in conformity to the depth of the 
depression (Plate II, fig. 1). Meanwhile, the lateral por- 
tions of the prophyllar tissue and associated rachis, which 
are free from pressure, bulge out as wings on either side 
of the penetrating spikelets. At this point in maize, lack 
of elongation by the internode or condensation forces the 
elongating spikelets to bend out and away from the cu- 
pule, finally diverging at right angles from it. This con- 
dition is in sharp contrast to that of teosinte and T'rip- 
sacum, as will be discussed later, where a slight elongation 
of the internode, as well as the rigid, sessile and solitary 
condition of the spikelets, leave no alternative for the 
spikelets but to become embedded more deeply into the 
rachis segment as a result of pressure from constriction. 
Teosinte and Tripsacum. The homology of the cupule 
lining to the prophyll is more obscure in teosinte and 
Tripsacum than it is in maize, because of reductions re- 
sulting from an extreme depression of the rachis segments 
in these relatives of maize. The lining of the hollowed 
rachis segments consists of very small lignified cells sim- 
ilar to those which line the cupule of maize, except that 
they are spread out more thinly over the surface of the 
cavity. As with the maize cupule, these cells of the lin- 
ing are smaller and more highly lignified than those of 
the rind. In the relatives of maize, a reduction in the 
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