SEROLOGY AND SYSTEMATICS 75 



other parent and is truly a hybrid. This work will be described more 

 fully in Chapter 15 (Hybrid Studies). 



In the older literature, there are some serological investiga- 

 tions which have been correlated with other criteria but not in a man- 

 ner which is wholly capable of resolving questions such as those 

 raised above. For example, Baldwin et al. (1927) studied the serolog- 

 ical interrelationships of a number of cross-inoculation groups of 

 legumes. Cross-inoculation groups are groups of species within which 

 certain nodule-inhabiting strains of bacteria may be cross-inoculated. 

 Generally, it may be assumed that the species belonging to a partic- 

 ular cross-inoculation group are rather closely related to each other. 

 In some cases a particular cross-inoculation group may also be affected 

 similarly by some pathogen; for example, in the cowpea group several 

 genera are susceptible to the bacterial spot disease. Using a variety of 

 reactions (including precipitin reactions and the Schultz-Dale tech- 

 nique) these investigators found that in general the serological re- 

 sponses were in agreement with cross-inoculation grouping. In the same 

 paper a summary of previous serological investigations of some genera 

 indicated agreement with the cross-inoculation group disposition of 

 the genera, and these investigations offered some support for the 

 validity of the serological method. A final precaution was taken to 

 establish that the reaction involved host-plant antigens rather than 

 bacterial antigens. Legume-seed antisera did not agglutinate the 

 corresponding nodule inhabiting bacteria. 



Recent botanical investigations in systematic serology at 

 Rutgers University begin with the work of Baum (1954) on the 

 Cucurbitaceae and by Johnson (1953, 1954) on the Magnoliaceae. 

 Subsequently, Hammond (1955a, 1955b) reported on serological in- 

 vestigations in the Solanaceae and Ranunculaceae, and Fairbrothers 

 (Fairbrothers and Johnson, 1959; Fairbrothers and Bouletta, 1960) 

 has investigated some grasses and certain species of the Umbel- 

 liferae. Since these investigations are quite similar in methodology 

 and approach, and in general do not introduce highly controversial 

 interpretations, only the Johnson work and the Hammond work on 

 the Ranunculaceae will be discussed. 



In Johnson's serological investigation of the Magnoliaceae 

 several genera were compared with Magnolia and then several species 

 of Magnolia were compared to establish intrageneric serological re- 

 lationships. The serological data are shown in Table 5-1. It has been 

 noted that the precipitin reaction was, in the Rutgers laboratory, 

 derived from calculating the area under the curve of photronreflec- 

 tometer readings at various antigen dilutions. At the generic level 

 the contention that Magnolia, Michelia, and Talauma form a natural 



