WEATHERWAX: SPIKELETS OF ZEA Mays 489 
tissues. At anthesis those of the upper flower are seldom visible, 
while those of the lower flower are relatively conspicuous even 
when such flower has a functional pistil. 
The pistil of the upper flower is not materially different from 
that of other grasses. .Guignard’s description is accurate. As 
Fics. 12-15.. Sections showing steps in the decline of the pistil of the male 
flower, X 60. 
he has pointed out (3, p. 43), the pistil seems to be developed from 
a single carpellary leaf. The duplex structure of the “silk” 
indicates that it may have resulted from the union of two parts, 
but there is no direct evidence of this. 
After the stamen primordia have been differentiated, the be- 
ginning of the pistil is left as a small, rounded protuberance. Near 
the base of this a ring of tissue begins to grow up and finally arches 
over to form the ovary wall (W, TEXT-FIGs. 9, 10, and PLATE 23, 
FIG. 3). Ultimately the edges of this come together at the top, 
but the union is never complete, a small opening to the inside, the 
stylar canal, being present at the top of the mature ovary (SC, 
TEXT-FIGS. 10, 11). In the meantime, a small projection grows 
up on-the adaxial side of the stylar canal, a little distance from the 
latter, to form the primordium of the “silk.” | 
