72 BIOCHEMICAL SYSTEMATICS 



serological approach. In any event the serological data were in general 

 ignored by the majority of systematists, though von Wettstein is said 

 to have regarded serological data as useful, within limits, in phylogeny. 

 Chester offers a quotation from the Swedish systematist Heintze as a 

 reflection of the opinion of many systematists: 



Serodiagnostic investigations have hardly contributed to a clearing up 

 of the relationships within the Cormophytes. By and large they only 

 "confirm" the errors of Engler and Prantl. 



With the passage of time details of the Mez "Stammbaum" 

 have faded from the memory of most of the relatively few people who 

 saw it. The illustration was copyrighted, and aside from its appearance 

 in the original article, has been published only rarely. It is difficult to 

 believe that the "Stammbaum" possesses much validity in view of the 

 current recognition of certain limitations of the early serological 

 methods. Yet, when higher taxonomic categories are compared sero- 

 logically, correspondingly, the sensitivity of the method may not need 

 to be as great to provide clues to relationships. 



Boyden (1942), in an important general review of serology 

 and systematics, discussed some of the methodological innovations in 

 use at that time, particularly the "photronrefiectometer," which is 

 essentially a modified densitometer. The Rutgers serologists (botanical 

 as well as zoological) are now using mostly densitometric measurements 

 of the precipitin reaction (Boyden and De Falco, 1943), but Moritz, in 

 Germany, is using a micromethod called micronephelometry in which 

 a beam of light passes through a microscope slide, containing the test 

 solution, mounted on a microscope. A photocell is attached to the 

 ocular position, and light reduction resulting from turbidity is recorded 

 through the photocell and an ammeter (Moritz, 1960). An interesting 

 point brought out by Boyden concerns the phenomenon of optimal 

 proportions. Briefly, it has been established that the amount of pre- 

 cipitate obtained with constant amounts of antiserum and increasing 

 dilutions of antigen rises from zero to a maximum then falls off again 

 to zero with considerable excess of antibody. As a result of this 

 phenomenon (for which several hypothetical explanations exist), one 

 must compare interactions over a series of dilutions. The optimal 

 proportion for different antigen preparations may vary significantly, 

 as indicated in Fig. 5-1. Since in most of the early serological work only 

 one proportion of antigen and antibody preparations was utilized, it 

 is obvious that the reliability of the method was accordingly lessened. 

 This disclosure cannot help but reduce the value of much of the early 

 serological work including, of course, that of Mez. 



