138 WEATHERWAX: MORPHOLOGY OF FLOWERS OF ZEA MAYS 
of the same plant, but such is not the case. Hunt (6, p. 146); 
Harshberger (1, p. 401), Collins (15, p. 3), and others say that 
self-pollination is possible, and my own observations are in accord 
with their conclusions. In securing pure lines for experimental 
work I have had occasion to self-pollenize individuals of about 
twenty varieties, and I have, in no case, had to have recourse to 
any means of pollen preservation. Contrary to the popular idea, 
I find that the period during which pollen is shed by any one plant 
extends pretty well over the time between the maturity of its 
first and last stigmas. 
Anthesis in the male inflorescence begins a short distance 
from the tip of the central axis, and a little later at the tip of 
each rachis, and the region of maturity of the flowers passe 
downward along all the axes simultaneously. The period of 
maturity is further lengthened by the fact that the two flowers 
in a spikelet do not mature at the same time, and a second wave 
of maturity and pollen shedding follows the first. Furthermore, 
the anther does not discharge all its pollen as soon as it is ripe, 
but lets it sift out slowly. The combined effect of all these 
conditions is to lengthen the period over which the plant is 
shedding pollen. 
The pistils near the base of the female inflorescence are the 
first to mature, and their stigmas emerge from the husk and 
become receptive usually about the time the first pollen is shed 
by the same plant. Many individuals are found, however, whosé 
stigmas are out before the maturity of the male flowers, and the 
reverse is also true of many individuals. In most of the kinds 
commonly cultivated, however, neither of these characteristics 
seems to be constant for the variety. It is possible that, if the 
order of maturity of the two inflorescences behaves in true Met 
delian fashion, this characteristic has been disregarded in hybridi- 
zation and selection to such an extent that it has not become fix 
for the variety. Self-pollination of an individual is rarely com 
pletely prevented in the commoner cultivated varieties by @ 
difference in the time of maturity of the inflorescences. 
But, in spite of the fact that self-pollination is possible and 
actually Occurs to a certain extent, it is clear that cross pollination 
is not only the common occurrence, but is necessary for complete 
