ZEA MAYS 133 



this type of inflorescence. One, advanced by Harshberger (8), sug- 

 gests that the lateral branches or rachids of a primitive inflorescence 

 were united or undiverged to form the ear. On the other hand, 

 Montgomery (11) maintains that only the central spike of the 

 primitive tassel has persisted to form the ear. An alternative 

 theory has been advanced by Collins (5) on the basis of his study 

 of seed hybrids between maize and Euchlaena. He suggests that 

 "the shortening and twisting of the axis of a single spike" may be 

 "a possible method of deriving a structure like the maize ear from 

 the inflorescence of Euchlaena." In all probability, none of these 

 explanations is complete and a final interpretation must await 

 further studies on the phylogeny of the grasses. 



The characteristic two-ranked appearance of the mature grains 

 on the ear is due to the manner in which the spikelets and their 

 flowers develop. This has been fully described by Miller (10) and 

 Weatherwax (19, lo) and the essential details are here summarized. 

 Just back of the meristematic tip of the young axis of the cob, 

 numerous primordia arise on its periphery. Each of these rudi- 

 mentary primordia, by an equal division, forms a pair of primordial 

 lobes which lie side by side in the same transverse plane; and these 

 in turn develop into the spikelets. The arrangement of the spike- 

 lets in transverse pairs is thus the result of the common origin of 

 their primordia from a single rudimentary primordium. 



The spikelet is two-flowered, but the lower flower is usually 

 abortive so that a single grain is produced in it. Since the spikelets 

 arise in pairs and a single grain is produced in each one, the grains 

 on the ear have the typical double-rowed arrangement mentioned 

 above. There are some notable exceptions to this arrangement, as 

 in Country Gentleman sweet corn, in which both flowers of the 

 spikelet regularly develop grains. This results in crowding and 

 an irregular arrangement. Other variations include cases in which 

 the grains are paired, connate grains where two kernels are more 

 or less completely united, and anomalous kernels with twin 

 embryos arranged side by side. Stratton (18) studied the develop- 

 ment of the double kernel in Zea Mays var. polysperma. In this 

 case, both flowers of the spikelet are functional and several types 

 of arrangement of the grains occur. In some instances, a pair of 

 separate kernels lie back to back; in others, connate seeds develop 

 with double kernels enclosed in a common pericarp, formed from 

 the coalesced ovaries of the two flowers. Semi-connate types 



