1913] Goodspccd: Nicotiana Hybrids 181 



capable of infinite divisibility and innumerable states of semi- 

 union with other correlated potentialities. 



All experimental studies in the physiology of heredity have 

 shown the necessity of consciously allowing a hypothetical term 

 to take the place of any visible outward expression of a certain 

 tendency — physiological in practically every instance— peculiar 

 to or inherent in an organism. This hypothetical term is de- 

 manded primarily for the formulation of a mathematical ex- 

 pression which can then express a multitude of situations in- 

 volving the tendency in question. This hypothetical term is 

 secondarily of real value in that it serves a-s a short-hand expres- 

 sion for this same tendency which may be utilized in referring 

 thereto in a considerable number of connections where mathe- 

 matical expression is not called for. It is, however, perfectly 

 evident that this hypothetical term has by reason of its associa- 

 tion with the living tendency to serve the above two ends, gained 

 absolutely nothing in the extent to which it actually represents 

 a tendency, peculiar to or inherent in a living organism. This 

 has many times been pointed out by East and others. The fact, 

 on the other hand, remains that the accumulation of experimental 

 results in the past 12 years that have been more or less readily 

 susceptible of interpretation according to the IMendelian notation 

 has resulted in a situation wherein hypothetical terms have abso- 

 lutely overshadowed the tendencies dealt with. The distinctions 

 between qualitative characters and quantitative characters rest 

 upon as hypothetical a basis and involve the use of hypothetical 

 terms as surely as does the use of such clearly hypothetical ex- 

 pressions as unit- character, factor, or gene. This is evident in 

 that we now know that certain qualitative characters and the ex- 

 planation of their mode of inheritance may rest upon the same 

 assumption or series of assumptions which originally was sug- 

 gested primarily to explain the facts concerned in the inheritance 

 of quantitative characters. The more carefully and "quanti- 

 tatively" the inheritance of qualitative characters is investigated, 

 the greater will be the field for the application of the assumptions 

 involved in Mendelian interpretations of variations which are 

 apparently continuous, if the experimental results can hope to 

 be explained according to the Mendelian notation. In other 



