BLENDING INHERITANCE 173 



general categories according to the degree of their 

 manifestation ; namely, total potency, partial potency, 

 and failure of potency. 



A further word of explanation for each of these 

 three kinds of potency seems desirable at this point. 



A. TOTAL POTENCY 



This is complete Mendelian dominance in which 

 even the heterozygotes produced by a simplex dose of 

 a character are indistinguishable phenotypically, that 

 is, by inspection, from the homozygotes produced by a 

 duplex dose of the same character. It is as if a single 

 bottle of black ink poured into a jar of water was 

 just as effective as two bottles of ink, in forming an 

 opaque fluid. 



Even in the cases of apparently complete dominance, 

 however, refined methods of examination or analysis 

 may make it possible to distinguish the duplex from 

 the simplex condition without recourse to breeding. 

 Darbishire has shown, in the case of Mendel's smooth 

 and wrinkled peas, that the two kinds of smooth prog- 

 eny from the Fj hybrid upon microscopic examination 

 show a difference in their starch grains that indicates 

 at once which is homozygous and which is heterozy- 

 gous. Moreover, in the power of absorption, hybrid 

 smooth peas (DR) are intermediate between their 

 pure dominant smooth (DD) and pure recessive 

 wrinkled (RR) parents. 



Blakeslee has demonstrated a chemical method of 

 distinguishing unseen genetic differences in the appar- 



