has suggested that the cupule, including its rachis-flaps, 
represents a prophyll adnate to the rachis. Before pro- 
ceeding with the evidence concerning Nickerson’s sug- 
gestion, the prophyll itself, will be defined and described. 
According to definition, the prophyll (pro-first ; phyll- 
leaf) is a leaf-like organ borne at or near the axil of every 
vegetative branch. It is characterized by two keels which 
lie adjacent to the margins of the main axis and by lat- 
eral wings which extend outward from each keel and 
clasp the branching shoot. In the case of the prophy]l! of 
an ear shoot in maize, these wings surround, overlap and 
sometimes fuse together at the base of the shank. When 
the wings are more narrow, as in vestigial glume maize, 
then pronounced lobes or auricles may appear at the base 
of each prophyll wing. The tissue between the two keels 
of the prophyll is much thinner and with fewer vascular 
bundles than that in the adjacent lateral wings. 
Nickerson (1954) has pointed out that the cupule dif- 
fers from the surrounding rachis in the orientation of a 
vascular system in its wings (rachis-flaps), in being often 
more pubescent and in having the capacity, in some 
cases, to be “‘peeled’’ from the rachis. Also, the cupule 
is often distinct from the rachis in being more highly 
lignified and sometimes of a different color. Color differ- 
ences are especially conspicuous when midcob color is 
present. This characteristic was described by Demerec 
(1927) and was later shown to be at the # locus (Man- 
gelsdorf, 1947). The R-midcob gene is responsible for 
a red or brown colored ring in the cob and a rind of cor- 
responding color on the culm. In the cob the color ex- 
tends from the colorless pith outward as far as, but not 
into, the cupules. On the barren faces between the lon- 
gitudinal rows of cupules, the outer edge of this colored 
area appears directly upon the epidermis of the rachis. 
The same barren area becomes green when development 
occurs in direct sunlight. 
[ 224 ] 
