254 Emerson. 



order tliat any part of the endosperm become waxy as a result of 

 mutation, a single H factor must have been lost or modified in the cell 

 from wliich the colored, waxy part of the seed developed. But this 

 single mutation would have left the other part of the endosperm not 

 only horny as it was but colored as well. In order that the horny 

 part of the endosperm be overlaid by colorless aleurone, a second 

 mutation must have taken place. Moreover tliis second mutation must 

 have affected at least two R or two C factors and might perhaps there- 

 fore be regarded as two distinct though simultaneous mutations. The 

 chance that three mutations might have occurred in one seed is ex- 

 tremely slight. But this is not all. Since the waxy and colored endo- 

 sperm constituted only a small part of the total, it seems likely that 

 the mutation from colored to wMte aleurone must have taken i)lace 

 very early in the development of the endosperm nucleus else a part of 

 the endosperm must have remained unaffected and consequently have 

 been both colored and horny, a combinatiou seen in no part of tliis 

 seed. At a somewhat later cell generation, the mutation from horny 

 to waxy condition must have occurred. Be it remembered, however, 

 that the waxy endosperm was associated with colored aleurone. Sijuul- 

 taneously with the last named mutation, therefore, there must have 

 occurred a mutation from colorless to colored aleurone, involving again 

 at least two R or two C factors and thereby to be considered perhaps 

 as two mutations. Tliis totals three, or perhaps we may say five, 

 mutations, including the loss and later regaining of two C or two R 

 factors or the modification and remodification of these two factors — and 

 all this within one seed notwithstanding that a single mutation of this 

 sort, if it is a matter of mutation at all, is expected about once in 

 10000 seeds! I cannot ask anyone to believe that all this has come 

 about, but there is one other possibility that must be examined before 

 the somatic— mutation hypothesis is discarded as a possible explanation 

 of this anomalous seed. 



The white seeded parent may iiave had an iiihil)it()r of aleurone 

 color. Tlie almost wholly white seeds constituting the ear on which 

 the seed in question was found strengthens this assumption materially. 

 The endosperm of this seed must then have been CCcRRrliiHhh, or 

 one or both C and R may have been homozygous. A mutation occurring 

 sometime after such white, horny endosperm had begun to develop, a 

 mutation involving the simultaneous loss or modification of a single H 

 and a single I, must necessarily have resulted in a white, horny seed 



