junei6, I9I9 Structure of Maize Ear 135 



The order in which these changes occur is by no means fixed, but taken 

 together they comprise all the changes necessary in deriving the maize 

 ear from the Euchlaena spike. 



In this series of intermediate stages nothing was observed that affords 

 support for either the fasciation or "reduced branch" theory of ear 

 formation. There is also evidence from the maize ear itself that the 

 association of alicoles into pairs is more fundamental than the linear 

 arrangement. 



In all the hybrids between maize and Euchlaena that have been ob- 

 served there has appeared no suggestion of either pod com or Zea ramosa. 

 Since it can scarcely be doubted that the peculiar characteristics of both 

 of these mutations represent the reappearance of ancestral characters 

 common to the Andropogoneae, it would seem that in crossing maize 

 ^nd Euchlaena, and thus calling forth a series of intermediate forms, we 

 are not returning to the point in the ancestry of maize where it became 

 differentiated from the Andropogoneae. 



Furthermore, if the stages shown in the hybrid plants w^ere to be taken 

 as indicating the path of evolution of the ear, it would be necessary to 

 assume that the central spike of the staminate inflorescence or tassel had 

 evolved separately and along different lines. The close homology 

 between the ear and the central spike of the tassel makes such an assump- 

 tion unreasonable. 



In the present article emphasis has been placed on the shortening and 

 twisting of the axis of a single spike as a possible method of deriving a 

 structure like the maize ear from the inflorescence of Euchlaena. This 

 has been done, not because the method is believed to represent the most 

 probable course of evolution, but because the present discussion has 

 been restricted to the evidence afforded by hybrids of maize and Eu- 

 chlaena, which seems to require such an interpretation. 



Facts of other kinds are more easliy interpreted by the theories of 

 fasciation and reduction of branches, but there are also facts that do not 

 seem to accord with any of the theories yet proposed. Until the appar- 

 ently contradictory evidence can be reconciled, it seems best to keep 

 the several possibilities in mind and await additional evidence before 

 attempting a complete interpretation. 



