THE PllVSlCAl. BASTS OF LIFE 45 



represents the sole, or even the primary, physical basis of 

 heredity, as maintained by s(mie investigators, is still an 

 open question; but as has earlier been indicated it seems 

 no longer open to doubt that the development of particu- 

 lar characters somehow depends upon the presence in the 

 nucleus of corresponding particular and separate heredi- 

 tary units ; and the conclusion loses nothing of its force by 

 reason of the fact that the precise nature of these units is 

 still unknown. We know fi'om the celebrated experi- 

 ments of Boveri and his successors that normal develop- 

 ment depends on the normal combination of these units."' 

 Conversely, genetic evidence is now opening far-reaching 

 horizons of future discovery by the accunmlating demon- 

 stration that no one of the nuclear units plays an exclu- 

 sive r(31e in the determination of any single character. It 

 has been proved that the individual unit often affects the 

 production not merely of one character but of many. The 

 converse probability is shaping itself that the production 

 of any single character requires the co-operation of sev- 

 eral or many units, possibly of all. I believe it is not a 

 great overstatement when I say that every unit may affect 

 the whole organism, and that all the units may affect each 

 character. We begin to see more clearly that the whole 

 cell-system may be involved in the production of every 

 character. How, then, are hereditary traits woven to- 

 gether in a typical order of space and time ? It is the same 

 old puzzle, made larger and more insistent, but not yet, so 

 far as I can see, brought nearer to its solution. We are 

 readv with the time-honored replies: It is an act of the 

 "organism as a whole"; it is a "property of the system as 

 such"; it is "organization." These words, like those of 

 Goldsmith's country parson, are 



"Of learned length and thundering sound." 



