BIOCHEMICAL STUDIES OF HYBRIDS 297 



present opportunities for the study of biochemical genetics of higher 

 plants rivalling those of microorganisms. For example, in a recent 

 paper, Tulecke (1960) has reported new data on the development of 

 tissue from Ginkgo pollen. This tissue is basically haploid though 

 some polyploidy appears. If extensive experimentation should lead to 

 a practical method of deriving haploid callus growth from pollen, one 

 major advantage is immediate. Furthermore, techniques exist for 

 separating such clusters of cells (by pectinase, for example), and 

 Steward et al. (1958) have succeeded in producing whole carrot plants, 

 apparently from individual cells. It is not beyond possibility that 

 clonal lines, established from single cells of dispersed haploid tissue, 

 may someday provide the combination of advantages inherent in 

 microorganisms. 



In an earlier section it was stated that, in effect, our knowl- 

 edge of biochemical pathways has emphasized the basic similarities in 

 the metabolism of diverse organisms rather than differences. Of nu- 

 merous examples supporting this view, the oxidative breakdown of car- 

 bohydrate, the structure of the nucleic acids, and the nearly universal 

 distribution of numerous co-enzymes are particularly significant. 

 Perhaps, partly as a consequence of a natural preoccupation with 

 unity in metabolism, comparative biochemistry is just beginning to 

 reveal its full potential in phylogenetic studies (for example, Florkin 

 and Mason, 1960). It is reasonable to expect that one must establish 

 the order before profiting fully from the study of biochemical innova- 

 tion in evolution. If extensive biochemical genetic studies in higher 

 plants become practical, we should expect an interest to develop in 

 comparative systematic biochemistry. More effort needs to be directed 

 toward elucidation of major metabolic pathways in the higher plants. 

 This knowledge should be extended to include the biosynthesis of sec- 

 ondary substances. 



One technique which may be expected to yield information 

 of predominantly systematic importance is that of the biochemical 

 study of hybrids. This chapter is devoted to a review of some hybrid 

 studies which are essentially biochemical in nature. The work is 

 widely scattered throughout the literature, and in a number of cases, 

 the original investigation was directed to some objective which did 

 not represent, basically, a problem in systematics. Because of this 

 fact, and the lack of any review of the subject to use as a point of de- 

 parture, the present discussion is inevitably eclectic. Many papers 

 included in this section concern classes of compounds already discussed 

 in previous chapters, and this pertinent background information is 

 not repeated. 



Perhaps one of the first "biochemical" studies of hybrids, or 



