form of a pulvinus, an axillary swelling which has become 
specialized for spreading these branches at the time of 
anthesis. ‘The tissues of the mature pulvinus suggest the 
primordium of an organ such as the prophyll, in that the 
swelling results from a proliferation of many small cells 
rather than from an expansion in size of individual cells. 
A study of the ontogeny of the pulvinus would be of 
interest in that leaf primordia (which would complete 
development) are usually initiated in the dermatogen or 
outermost layer of cells, although this condition might 
not necessarily apply to reduced leaves. Vascular devel- 
opment in the pulvinus, like that of the glume cushion, 
appears to be a part of the rind of the rachis. 
Higher up in the staminate rachis or central spike of 
the tassel where the axillary buds are manifest as binate 
spikelets rather than as elongated branches, the rudimen- 
tary prophyll usually appears as a scab-like growth on 
the rachis or may be entirely reduced. 
In the pistillate rachis, it is the lining of the cupules 
which seem to represent the prophyll. The small cells 
of this lining are very similar to the small cells of the 
pulvinus, and the physical differences in the external 
shape of these structures may be attributed to differences 
in compression during development. 
The depression of the rudimentary prophyll and asso- 
ciated tissue is even more extreme in the relatives of 
maize. ‘The result is a deeply hollowed, cupulate rachis 
segment which is lined with a thinner layer of ‘‘prophy]- 
lar’? cells and has a distorted and reduced vascular sys- 
tem. Such effects are extreme in teosinte rather than 
intermediate between its putative parents, as might be 
expected if teosinte is a derivative from a hybrid between 
these other two species, because the extreme compression 
responsible is a hybrid product of combining two other 
characters. Accordingly, when the erect and_ sessile 
[ 29 ] 
