16 
Indiana University Studies 
(Figs. 37, 38). In so far as can be determined from the 
material at hand, the spikelets closely parallel those of Poly- 
toca and Sclerachne in structure. 
Probable Relationships 
A tabulation of similarities between the American Maydeae 
and those of the Orient gives an apparently valid basis for 
placing them in the same group at least for convenience. But 
to assume a close natural relationship among the genera is 
probably not warranted by the most significant evidences. 
Monoecism is the chief unifying characteristic of the 
Maydeae, but it is the result of a very general tendency thru- 
out the Gramineae, especially the Panicatae, toward the differ- 
ential abortion of parts of the flower. The occurrence of mon- 
oecism, dioecism, or polygamy is so common in the grasses 
that the sexual condition cannot be regarded as a strong 
criterion in the absence of good support of other kinds, or 
in spite of evidences of inconsistency. 
In all the Maydeae the fruit is wholly or partly covered by 
an indurated shell, which is an especially attractive superficial 
indication of relationship. Its relative absence in Zea may be 
explained by the unusually complicated covering of husks, or 
as a result of conscious selection by man. But this general 
occurrence of a hard shell is a deceptive analogy, rather than 
a homology. The indurated structure is a combination of a 
glume and an alveolus of the rachis in Tripsacum and 
Euchlaena, a spathe in Coix, and a glume in Polytoca, 
Sclerachne, and Chionachne. A tendency toward induration 
of something connected with the fruit seems, therefore, to be 
all that the genera have in common, and this is possessed by 
so many other genera of grasses as to be of little significance 
in determining tribal relationships. 
Geographically the Maydeae are sharply divided into two 
groups, one in each hemisphere, and neither has ever made 
its way into the field of the other without the help of man. 
On the other hand, all the genera of each group overlap suffi- 
ciently in distribution to suggest an American progenitor and 
another in Australasia. 
The comparative morphology of the genera suggests the ar- 
rangement of the Maydeae in four categories of phylogenetic 
relationship : 
