Kempton: ijranched Ears in Maize 



245 



ears in flowering it would seem to l)e 

 the bettsr nourished. 



It seems not unreasonal)le to suppose 

 that vigor would increase or favor a 

 tendency to branch while severely un- 

 fa\'oral)le conditions certainlv would re- 

 sult in the suppression ot branches. 

 However, if th:s were the whole ex- 

 ])lanation of the variability in branch- 

 ing, the general unfavorable conditions 

 which cattsed supi)ression of branches 

 should result also in a reduction of the 

 size oi the ear with the result that un- 

 branched ears of progenies grown from 

 a branched parent would be smaller 

 than the branched ears in t\v^ same 

 ])rogenv. Such does not prove to 

 be the case ; in fact, the contrary 

 seems to be true and if external en- 

 vironment is to b? considered as a fac- 

 tor in the production of [tranches it 

 must l)e assumed that this factor af- 

 fects only l)ranching rather than vigor 

 in general. 



While environment may be an im- 

 portant factor in the suppression or de- 

 velopment of branches, adjacent plants 

 in a row undoubtedly have a very 

 similar environment and* when one 

 plant produces branched ears, and the 

 next unbranched ones, the change must 

 be in the nature of a threshold effect: 

 where small environmental fluctuations 

 have acted in the same direction with 

 factors controlling branching. If this 

 l)e true then the branched progenies of 

 unbranched ears, produced in progen- 

 ies grown from branched ears, would 

 be expected to have fewer branched- 

 eared plants than the progenies grown 

 from their branch-eared sibs. 



An examination of the pedigree 

 chart shows that the progenies from 

 unbranched ears in the early genera- 

 tions had fewer branched ears than the 

 progenies from branched sister ears 

 but that in the later generations no 

 such difference is n'iaintained. In fact, 

 the only unbranched progeny in the 

 later generations, directly descended 

 from the original branched ear. was 

 from a branched-eared parent. There 

 is little to indicate, therefore, that in 

 the later generations the difference be- 



tween the branched and unbranched 

 condition is heritable and the failure 

 to develop branches in this ])articular 

 line must be attributed to accidents of 

 development. 



As the chart shows, five progenies 

 were grown from the self-pollinated 

 ])lants of the original sowing and with 

 a single exception all the branched 

 ears thus far ol)tained are descended 

 directly from only one of these five 

 ])rogenies. 



The exception ajjpeared in the third 

 generation of contmuous inbreeding of 

 the line marked X in Figure o. The 

 pedigree of this line is too extensive to 

 ])ublish, but 104 ])rogenies have been 

 grown. 103 of which have produced no 

 branched ears and the other, one plant 

 with a branched ear and twenty-six 

 plants with normal ears. 



Seventy-four progenies representing 

 six generations have now been grown 

 from the eighty-eight plants of the 

 progeny that produced the first 

 branched ears and from these progenies 

 the following generalizations are possi- 

 ble : 



The progenies of branched-eared 

 plants have, with a single exception, al- 

 ways ])rodticed some branched-eared 

 plants and since the percentage of such 

 jilants ustially is low it is not certain 

 that this exceptional ]M-ogeny which 

 comprised only eighteen ])lants. would 

 not have gi\'en some branched ears had 

 a larger population l)een grown. In 

 this case if the expected ratio is as- 

 sumed to be 4.(S unbranched to 1 

 branched ( the , ratio closely approxi- 

 mated in sister progenies) then the 

 observed ratip- of 18 normal to 

 branched' plants departs from the as- 

 sumed by an amoimt which would be 

 expected to occur as the result of 

 chance about once in fifteen times. In 

 the entire pedigree there are thirty-five 

 cases where progenies have been grown 

 from self-pollinated normal ijlants that 

 had branched-eared sibs. These prog- 

 enies are not of the branched livie 

 shown in Figure 5 and if some of the 

 unbranched ears of these progenies are 

 heterozygous for branching two classes 



