WEATHERWAX: THE EVOLUTION OF MAIZE 323 
accompanied by another male or sterile one; and each female 
spikelet is characteristically alone, has an indurated outer glume, 
and is sunken into the rachis. No functionally bisexual spikelets 
have been seen, but it must be emphasized 
that all are structurally so. 
MorpPHOLOGY OF TRIPSACUM 
A number of species of Tripsacum are 
native of various parts of America, but the 
best known is Tripsacum dactyloides L., the 
gama grass of swamps and stream banks of 
the central and southern parts of the United 
States. Being the only species available for 
my work, it is the basis of my conclusions 
for the genus. 
Tripsacum dactyloides (FIG. 30) is peren- 
nial by means of a branched rhizome, from 
the nodes of which arise the aerial shoots. 
Many of these are sterile, and their stems 
are so short that only the leaves appear above 
the ground. In early summer, however, some 
of the shoots elongate for flower bearing and 
show the adult structure. These stems attain 
the height of four to six feet and resemble 
somewhat those of maize or teosinte. The 
flowering period continues for two or three 
months. The main stem bears a branch at each node, and this 
has secondary and even tertiary branches. The main stem is 
terminated by a panicle, and each branch by a spike or a pan- 
icle. Erect or curving until after flowering, the stems are, by 
means of some growth-mechanism near the base, caused to lie 
prostrate by the time the seeds are mature. 
Inflorescence—The male spikelets occupy the terminal and 
the female the basal part of the same spike (Fic. 31). The mode 
of branching of the panicle is similar to that in the male inflores- 
cence of Euchlaena, There is no evidence of any central spike, 
all the branches being much alike. 
There is a very evident tendency for the highest inflorescence, 
Fic. 29. A mixed spike 
of teosinte. 
