No. 642] 



NATURE OF BUD VARIATIONS 



69 



that the non-inheritance of the da^k-cro\\^l type is clue to 

 the accident that it occurs in epidermal tif^sue outside the 

 germ tract, 



Eecent investigations of variegated maize by Eyster 

 and Anderson have established the fact that somatic mu- 

 tations afiPecting small areas occur much more frequently 

 than those affecting large areas. Since a mutation aris- 

 ing in a single cell late in development obviously could 

 not affect so large an area as one originating earlier, it 

 follows that mutations in variegated maize occur with 

 increasing frequency in the later stages of ontogeny. It 

 is true, as pointed out by Muller ( IDl'O), that given a con- 

 stant rate of mutation throughout all stages of ontogeny 

 and granting that one cell is as likely as another to mu- 

 tate, mutations should appear more frequently in the 

 later stages of development because of the fact that there 

 are then many more cells in which mutations nniy arise. 

 But Eyster and Anderson have found that the increase in 

 the frequency of occurrence of mutations during the 

 progress of development is accelerated far beyond ex- 

 pectation based on the increase in numboi- of cc^lls. 



This ])ehavior is strongly suggestive o!' ;i ])n>- rt--iv(' 

 acceleration in the mutability of the Nni icu.it inn urn. a^ 

 (h'velopnuMit proceeds. It is much loo mvly io ><i\' 

 whelliei- tliis ])rogi-ossive change, if such it l)e, is inherent 

 in ihe (.ruaiiiz.-ilion of the gene itself, as suggested by 

 And.T^oii Ddnerec, or whether it is a response to 



progri s<i\-e ehniiges in physiological and environmental 

 relations, l^erliaps the assumption of an equal chance of 

 mutation as l)etween any two cells is without sufficient 

 wan-ant. Possi])ly there is a time (^lenient to be taken 

 into account, as noted by Muller ( l!>i'i> ). A< cell division 

 becomes progressively retarded in tii.' Inle uTowth stages, 

 may not each cell be exposed f..,- ;ni in.Mv.inndy longer 

 period of time to the cimnce ol' mulalion.' Perhaps it 



