326 WEATHERWAX: THE EVOLUTION OF MAIZE 
Some of the stems of Tvipsacum live underground, thus making 
the plant perennial, a condition which, in some of the species at 
least, is associated with the swamp habitat and limited seed 
production. When Euchlaena grows in a swampy place, it has a 
tendency to assume the perennial habit by means of prostrate 
34. Diagram of a cross section of one internode of a male spike of maize or 
teosinte, showing the rachis, R, with one sessile, S, and one pedicelled, P, spikelet, 
IG. 35. Section of an internode of a female spike of Tripsacum or Euchlaena. 
showing a functional sessile, S, and a rudimentary pedicelled, P, spikelet imbedded 
in the rachis, 
stems rooting at the nodes; its seed production, however, seems 
in no way impaired by this habit. Maize produces a large number 
of viable seeds and has no tendency to become perennial. 
The general inflorescence of the group is a panicle with a 
central spike and lateral branches, like the tassel in maize. In 
most of the inflorescences some parts of this general structure are 
lacking; in the maize ear it is the lateral branches, and in the 
teosinte tassel and the inflorescence of Tripsacum it is the central 
spike; in the female spike of Euchlaena all that is present is a 
single lateral branch. The spikelets occur usually in pairs, but 
sometimes in larger groups, in all the inflorescences. 
The spikelet has two glumes and two florets. Structurally 
the flowers are as in the typical grass, but the regular suppression 
of some of the essentials makes all the flowers functionally uni- 
sexual. Tripsacum has two feathery stigmas, but the homologue 
of these in Zea and Euchlaena is the silk, a fasciated organ divided 
at the tip. 
THEORIES OF THE EVOLUTION OF MAIZE 
As has been noted by way of introduction, several theories | 
have been advanced to explain the origin of the maize plant or 
some of its parts; and it is appropriate here to examine in a critical 
way some of the more prominent of these. 
