junei6, I9I9 Structure of Maize Ear 133 



A further shortening of the rachis brings about the next stage, which is 

 that of a lo-rowed ear. Intermediate stages are more common during 

 the acquisition of this stage, and when they occur the seeds, as might be 

 expected, are not arranged in regular rows. 



With these facts in mind, the spike can be understood as composed of 

 opposite or yoked ahcoles, each with a pair of spikelets. These yokes 

 are superposed, and as crowding increases there results a further twisting 

 and the formation of a more complicated spiral. With seeds of a uni- 

 form size a compact spiral would result in the formation of longitudinal 

 rows, though these might not run exactly parallel to the axis of the ear, 

 as, indeed, they seldom do even in ears of maize. 



MORPHOLOGY OF THE MAIZE EAR 



It has been shown that the intermediate forms that appear in hybrids 

 between maize and Euchlaena afford no support for the f asciation theory. 

 Evidence from the ear of pure maize may now be presented. 



If a number of four-rowed branches were forced together and their 

 axes united, the conditions found in an ear of maize might result (see 

 fig. I, B). There is, however, evidence in the ear itself that it is not 

 constructed in this way. 



It is not an uncommon occurrence for an ear to drop rows. For 

 example, there may be 12 rows at the base and only 10 rows at the tip. 

 A study of how this transition is made throws light on the morphology 

 of the ear. In the first place, the loss is almost invariably two rows, 

 and both are lost at the same distance from the butt of the ear. There 

 is no region with an odd number of rows. A normal ear is made up of 

 a series of paired rows and this is usually accepted as an adequate explana- 

 tion of the fact that the number of rows is always even. A pair of rows 

 is looked upon as the fundamental structural unit of the ear, a view in 

 accord with the theory of fasciation. Since two rows are dropped at 

 once, it might be expected that the interrupted rows would be adjacent. 

 This would follow from the suppression of a pair of rows representing 

 the sessile and pedicelled spikelets arising from a single series of alicoles. 



There is, however, abundant evidence to show that rows are usually 

 interrupted by the abortion of pedicelled spikelets only. This can be 

 seen in abnormal maize tassels in which the base of the central spike is 

 pistillate, forming in reality a section of an ear. At the place where the 

 transition occurs it can be seen that the sessile spikelets are more per- 

 sistent and produce larger seeds. ^ 



' With the idea of determining to what extent differentiation between pedicelled and sessile spikelets 

 persists in the fully developed maize ear, the weight of each of the two seeds from individual alicoles was 

 compared. An ear of flint corn was chosen in which the alicoles were clearly marked and the individual 

 seeds were carefully weighed. There were 135 alicoles with two comparable seeds. The average weight 

 of the individual seeds for all the seeds was 430 mgm. The average difference between the seeds of an alicole 

 was 21.0 mgm. ±19.5. 



It would appear, therefore, that if there was any consistent difference between the weight of the seeds 

 borne in pedicelled and sessile spikelets in this ear, the difference must have been something less than 

 S per cent of the weight of the seed. 



