288. WILLIAM LAWRENCE TOWER, 



is a potash feldspar, is the potash a mineralogical unit character? 

 It seems to me that the problem of the constitution of natural 

 substances is the same in both living and non-living substance, and 

 that there is in living substance something very much like that 

 which is found in non-living substance in the combining of attri- 

 butes from diverse sources into compact and distinct wholes. 



Because a character is sharp and distinct, or may be apparently 

 removed, is no necessary reason for supposing that it may be 

 taken away as an entity, and no reason whatsoever for believing 

 it to be conditioned by a subsidiary mass; rather, we must re- 

 gard an organism essentially as we would look upon any inorganic 

 substance, as a mass of matter in which the unit is the individual 

 with its array of attributes or qualities, or its specific characters. 

 It is certain, however, that there is adequate evidence to prove 

 the truth of the situation as described by the Mendelians as far 

 as the behavior of the attributes is concerned ; but the basis and 

 cause of this behavior is entirely unknown, and must remain 

 unknown until we have replaced by fuller knowledge the present 

 crude ideas of the constitution of living substance. 



The situation which has developed in the last few years at 

 the hands of the Neo- Mendelians themselves is interesting. 



From the simple conditions discovered by Mendel there has 

 arisen through the work of the last decade an array of observa- 

 tions tending to show that the Mendelian phenomenon is not 

 in many instances as distinct and simple as one might wish, 

 and at present divers kinds of variability in the behavior of 

 characters are described and attributed, in some instances, to 

 several different kinds of latency, to gametic coupling, to vari- 

 able potency, to variable dominance, and so on. The situs tion 

 essentially is this, that as investigation has progressed it has been 

 discovered that not one, but a host of determining factors (I 

 use the word factor as meaning something which makes possible 

 a given result, with no idea expressed or implied as to the nature 

 of this factor) are operative in the production of alternative in- 

 heritance; and in the attempt to preserve the letter of the law 

 of Mendelian theory of unit characters with segregation in 

 gametogenesis, a host of hypotheses have been developed in order 

 to save the original theory. 



