No. 643] SEROLOGICAL PHENOMENA 



123 



Among interesting facts that come to light in Miss 

 Wakeman's summarization may be mentioned the fol- 

 lowing: all organic pigment molecules are unsaturated; 

 the quinone grouping is one of the best known of the 

 chromophorous groups; by far the largest number of 

 plant pigments arc referable to hydrocarbons of satura 

 tion C„H,«-u and CJL,,-,,,; and finally, that it is the 

 relation of the chromophorous groups to each other and 

 to the rest of the molecule, and not their mere presence 

 in the molecule, that postulates color in a substance. 



I may seem to have dwelt unduly upon pigmentation in 

 plants "but 1 have tried to go into the matter only suffi- 

 ciently to give a glimpse of some of the real conditions 

 which underlie some of the " unit-characters " we are 

 .iuggling about in genetics, and around which we are 

 attempting to frame hypotheses of evolution. Color, per- 

 haps more than any otiior oiu^ thing, has in recent years 

 been utilized for gcnetical obM-rvation.-^. And when it 

 known that in numy ca^e. (M.h)r i- merely a functu)n 

 of the degree of oxidati(m of some fundamental com- 

 ])(>nnd, or'the introduction or subtraction of some hydro- 

 carbon radical, it does not tax the imagination to conceive 

 of how it is po^.il.le to have -orie^ of color - character^ " 

 that in the parlan<-c of .M-ani.- ,-v.>lution rci'iv^mt ortho- 

 genetic series. A- -iniiilr a matter a- the relative degree 

 of oxygen supjil} . in (iltal>!.\' deterinined liy the amount ot 

 an oxidase ])re>eiil. i!ia>' aeciumt lor \arioii> -taue-- <> 

 color. It is manifeM, iiK.reoxer. that in a tiiven urnnp 

 there might easil\- be a tendency towar<l im-rea-e in o\i- 

 dase-production. u'lieh if pie^ent une.,nally m ditlerent 

 collateral line^ ini-ht tiive n- juM the un. ven .-nndition, 

 with different -peeler Mandiii- at dilVeivnt lexrU ot ex- 



