74 



THE AMEBIC AX X AT U BALI ST [Vol.LVI 



nature as that noted above for Drosophila gynandro- 

 morplis. In crosses in which recessive alenrone and 

 endosperm characters are contributed by the female 

 parent and their dominant allelomorphs by the male 

 parent, spots of the recessive (maternal) aleurone color 

 are underlaid by the recessive (maternal) type of endo- 

 sperm when the genes for these aleurone and endosperm 

 characters are genetically linked, that is, when they are 

 carried in the same chromosome. On the contrar\-, simi- 

 lar recessive (maternal) aleurone-color spots are always 

 underlaid by the dominant (patemal) type of endosperm 

 when the genes are not linked, that is, when they are 

 carried in non-homologous eliromosomes. Tlie fact that 

 linked genes separate out simultaneously while non-linked 

 ones do not do so supports the view that mosaic seeds are 

 the result of some chromosome aberration sucli as elimi- 

 nation or non-disjunction, and renders untenable the 

 earlier hypotheses of incomplete fusion of endosperm 

 nuclei suggested by Correns and by Webber and also that 

 of gene mutation proposed by myself. 



The work with aberrant maize endosperm has fur- 

 nished an opportunity to study the frequency of chromo- 

 some aberrations in a specialized tissue. The a\ ailable 

 data show that when a single cliromosomc nloiu^ is con- 

 cerned, about one mosaic seed occurs in cvcrx- 4l'i) ^<.,m1<. 

 If the other two homologous chromosomes of .•iii) (uic sd 

 are involved as frecpiently and if any one of ilif im t dip- 

 loid chromosome sets is as likely to be involved as any 

 other one, one case of a])eri-ant chromosome behavior 

 should occur in about e\'ery fourteen seeds. Tliere is 

 some evidence, though not ('(mvincing as yet, that in dif- 

 ferent strains of nialzo cliromosome aberrations may 

 occur witli strikingly different frequencies. In one cul- 

 ture in which only a single chromosome could have been 

 involved in the origin of mosaic seeds, as many as twenty- 

 five such seeds have been observed on a simple ear of aj)- 

 proximately 500 seeds, or one foi- each I'l) seed-. If tiiis 

 behavior proves to be a constant ..iie in ihi- Mi-ain and it* 

 the other -Jll ehi-onio<ome> h, have in like manner, it 

 should funii-h e\rclieni maierial \nv c.M ..h^u-icnl invr-ti- 

 gation. :\lonov(u-, the po>-il)ility of the existence of 



