132 Journal of Agricultural Research voi. xvii. xo. 3 



TRANSITION FROM A TWO-ROWED SPIKEJ TO A MANY-ROWED EAR 



The pistillate inflorescence of Euchlaena may be looked upon as a two- 

 rowed ear. In hybrids between maize and Euchlaena the initial step from 

 such a two-rowed ear to one with four rows may be made in two quite 

 different ways. The more common method is for the pedicelled spike- 

 lets, which are suppressed in Euchlaena, to reappear. This converts 

 the flat two-rowed spike into a flat four-rowed spike, the condition that 

 obtains in the first generation of the hybrid (PI, 17, B). 



In some instances, however, another method is followed. Alternate 

 intemodes of the spike become shortened until the alicoles, each with a 

 single spikelet, are yoked in pairs, the members of which stand opposite 

 or nearly so. The rachis then twists until each pair of alicoles, instead of 

 standing over the one below, stands at right angles with the pair immedi- 

 ately above and below (Pi. 16, D). This results in a square four-row ear. 

 The pairs of alicoles are crossed and fitted into each other in a way that 

 has suggested the name "saddleback" for this type of spike with four 

 rows of alicoles. 



In some instances still another step is taken before the spikelets are 

 doubled in the alicole. The rachis is still further shortened and twisted, 

 resulting in a six-rowed ear. Six-rowx-d ears are sometimes found in 

 which both sessile and pedicelled spikelets are developed. In such cases it 

 appears that the definite relation which ordinarily exists between yoked 

 alicoles has been lost, and starting with the flat four-rowed ear every third 

 alicole has slipped around so that it occupies a plane between the other 

 two, which in turn are slightly displaced (PI. 17, C). 



Returning now to the more common form of a four-rowed ear, it is to 

 be noted that the spike is four-rowed and the pedicels have been short- 

 ened, though the distinction between sessile and pedicelled spikelets can 

 still be made out with certainty. The rachis also has been shortened 

 and forced into a series of sharp angles and as a result of such crowding 

 it has now begun to twist (PI. 17, A). 



The next clearly marked stage is the eight-rowed ear. The shortening 

 of the rachis has continued, with increased crowding and twisting of the 

 axil, forcing the alicoles, each bearing a pair of spikelets, to slip past one 

 another into the unoccupied spaces of what were the upper and lower 

 sides of the original horizontal branch. This is again a saddleback type, 

 with the alicoles associated as in the square four-rowed ear described 

 above, though each alicole contains two spikelets instead of one (Pi. 15, F). 

 Intermediate stages between the flat four-rowed ear and the eight-rowed 

 saddleback stage can sometimes be found where the twist is not quite a 

 quarter turn, but all such appear to be unstable. The saddleback, on 

 the contrary, is stable and will sometimes be shown consistently through- 

 out a plant of the second generation (PI. 18). 



