150 



THE AMERICAN NATURALIST [Vol. XLV 



zygotic nature being necessary for " mottling" in some 

 special bean-hybrids, may at first glance favor the idea of 

 * ' spotted conditions ' ' being due to irregular segregation 

 or to different repartition of color-determining factors in 

 the tissues in question. But a closer examination seems 

 to vindicate the real existence of special "spotting 

 factors. ' 1 The very interesting researches of Lock as to 

 the "Inheritance of certain invisible characters in peas" 

 have clearly pointed out a "spotting" factor or a 

 "pattern "-determiner in peas, independent of any color- 

 manifestation. It must be borne in mind that a multitude 

 of characteristic epidermal "patterns" are found in 

 animals and plants, these patterns concerning all epider- 

 mal manifestations and often showing a widely fluctuat- 

 ing variability. As to the realization of all such spots it 

 might be suggested that in neighboring parts of the devel- 

 oping epidermal tissue some little difference of ambient 

 conditions may inhibit or even release reactions, the alter- 

 nation of which produces the spots. 



The whole case seems to be somewhat analogous to the 

 merely phen atypical phenomena of attentat ire variability 

 first pointed out by De Vries, e. g. f the alternation of 

 decussated and contorted stems of Dipsacus. Here we 

 touch the highly suggestive idea of "sensible periods" in 

 ontogenesis or histogenesis emphasized with so good 

 experimental arguments by De Vries. Of course there 

 must be a genotypical fundament for the existence of the 

 alternating character in question, e. g., for the particular 

 nature of the surface of the spots (or for the contortion 

 in Dipsacus, etc.) ; strains without such genotypical 

 fundament will not be spotted (nor produce contorted 

 individuals at all).— These remarks are made only to 

 point out that Morgan may have exaggerated a little his 

 criticisms as to "spotting factors," but I confess that this 

 question is in need of closer analysis. 



Then the problem of pure or impure segregation may 

 still be open; but the tendency in modern genetics goes 

 certainly in the direction of establishing pure segrega- 



