surface or lining of the cavity. Such a process of cupule 
formation, by a hypothetical splitting of the pulvinus, 
serves to illustrate the similarities of the structures in- 
volved. It does not represent a plausible explanation for 
the origin of the cupule in terms of ontogeny, as will be 
noted later. 
This relationship between pulvinus and cupule lining 
is also revealed by intergrades between these structures 
in tunicate (Zw gene) and other variants of maize. The 
tunicate cupules are usually shallow because of small 
wings and, in some cases, the ‘‘cupule’’ may be elevated 
above the adjacent rachis in such a way as to appear like 
a flattened pulvinus. One such type of tunicate cupule 
from a twelve-rowed ear of Argentine popcorn is illus- 
trated in Plate LV, fig. 4. The hairiness and distribution 
of small cells in this type of cupule produce a striking 
resemblance to that of the pulvinus (Plate IV, fig. 1). 
This condition differs from the typical cupule (Plate ITI, 
fig. 1) in having all of the rind bundles crowded into cor- 
ners between the cupules rather than dislocated into flaps. 
When tunicate cupules lack such vascularized wings, they 
may be ‘‘peeled’’ from the rachis. 
Other circumstantial differences may appear during 
the development of the pulvinus and cupule lining. Fer- 
tilization is accompanied by a metaxenial stimulation for 
the deposition of lignin in the small cells of the cupule 
lining, while the corresponding cells of the pulvinus 
eventually shrink during aging of the plant. Further, 
the cupule or its lining is embedded into the main axis 
or rachis, while the axillary pulvinus usually expands 
along the axis of the primary branch. But the primary 
branches of the ear are reduced to binate spikelets which, 
in certain ears of tunicate maize, may be associated with 
pulvinus-like swellings rather than cupules. Finally, the 
pulvini in certain highly condensed and compressed tas- 
[ 22] 
