184 University of Calif ornia Puhlications in Botany [Vol.5 



of independently heritable units for their somatic expression. 

 These interacting units may be looked upon as the substances en- 

 tering into a reaction which is represented at a point of equil- 

 ibrium by an outward, visible, seemingly or truly indestructible 

 "unit-character" peculiar to an organism. The individual re- 

 acting substances are separately inherited but may be so linked 

 (a chemical affinity) in the case of certain characters that the 

 same reaction will reach the same point of equilibrium time after 

 time and we then appear to be dealing with a unit distinct and 

 indestructible. Such analogies (cf. in this connection Moore, 

 1910 and 1911) supply a limitless field for speculation yet 

 it may be interesting to note that increase of size and pre- 

 cocity of somatic characters due to heterozygosis might be 

 concerned with an increase in the rapidity of growth reactions 

 caused by an increase in amount of reacting sustances. An atti- 

 tude in general analogous to the above is taken by East (1912, 

 p. 648) with reference to the changes in the expression of a 

 character under the stress of what he refers to as "modifying 

 conditions both external and internal" — "when external we 

 recognize their usual effect in what we call non-inherited fluctua- 

 tions, when internal we recognize their cause in other gametic 

 factors inherited independently of the primary factors but 

 modifying its reaction during development." In so far as this 

 is an assumption which seems to postulate a limitless extent of 

 organic complexity as the fundamental basis for those tangible 

 characters we seem to see in an organism and draws an analogy 

 between chemical reactions and the interrelations of these "fac- 

 tors," the above is "a physiological conception of heredity." 

 On the other hand if it is to become a question as to how many 

 separatelj^ inherited tendencies contribute to the entity which 

 we loosely speak of as a "unit-character" the logical end of the 

 inquiry will be found to lie in a biochemistry of the individual 

 cell (cf. Czapek, 1911, ch. 10). 



It is well to bear in mind in connection with such elusive con- 

 siderations as these that as we "bid farewell to the broad day- 

 light of observation" we at once proceed to "enter the dark and 

 treacherous alleys of inference." Observation, however, has re- 

 sulted in the accumulation of certain experimental results the 



