PAIRS OF CHARACTERS 139 



possession of a specific character, this specific 

 character meets nothing in the other organism 

 corresponding to it, and the result is a permanent 

 blend. Such crosses are called unisexual. But if 

 one organism is crossed with another from which 

 it differs in the possession of a varietal character, the 

 particular character in a patent state in one organism 

 meets the same character in a latent state, in the 

 other organism, and the result may or may not be 

 a blend, but is invariably segregation. These crosses 

 are called bisexual, or balanced crosses, the latter of 

 which is a much better term. Prof, de Vries's theory 

 of the nature of the Mendelian pair differs from the 

 presence and absence hypothesis in that, according 

 to him, the pair consists of a character in an active 

 or patent state (dominant) and the same character 

 in a latent state (recessive) ; whilst according to 

 the other theory the dominant member of a pair of 

 characters consists in the presence of something 

 and the recessive in the complete absence, not the 

 latency, of that something. It is premature to hold 

 the scales between these two before a much greater 

 body of evidence bearing on the question is available. 

 The investigation designed to furnish this evidence 

 must start from a perception of an essential difference 

 between the two theories ; the most important of 

 these, in my opinion, is the difference, according to 

 the two theories, between the constitution of the 

 recessives. According to the one theory, the 

 recessive is the dominant character in a latent 

 state ; according to the other, it is the absence of 



