BIOCHEMICAL STUDIES OF HYBRIDS 315 



useful in similar studies since its advantages are basically those of 

 paper chromatography. Thus gas chromatographic "fingerprints" of 

 individual plants may prove to be feasible even when the available 

 material is in small amounts. 



Specimens of P. attenuata contained much a-pinene but 

 practically no ^-pinene. P. radiata had both a- and /3-pinene with the 

 latter in excess. In both artificial and putative hybrids, both pinenes 

 were present, with a-pinene in excess. Thus the oil character of the 

 hybrids was essentially intermediate. There was no apparent build 

 up of minor constituents among the hybrids. Morphological charac- 

 ters used as criteria were not specified in detail, but the individuals 

 with hybrid oil character were said to be morphologically intermediate. 



An interesting biochemical study of Phaseolus hybrids has 

 been reported by Schwarze (1960). He had previously described cer- 

 tain dwarfed hybrids, which appeared together with nearly normal Fi 

 hybrids, of Phaseolus vulgaris X P- coccineus. These dwarfed hybrids 

 contained less chlorophyll, less protein, more peroxidase and poly- 

 phenoloxidase, less of flavonoid and simple phenylpropane derivatives, 

 less lignification, and increased breakdown of lAA and tryptophan. 



Examination of the leaf flavonoids of the two species of 

 Phaseolus revealed four flavonoids in P. vulga?is and four different 

 flavonoids in P. coccineus. The hybrids, in contrast, exhibited spots 

 on the chromatograms equivalent to all eight parental flavonoids plus 

 four additional spots. Schwarze stated that actually the four hybrid 

 flavonoids did occur in minute but perceptible quantities in the 

 P. coccineus parent. Young leaves were richer in flavonoids than were 

 older leaves. The "disturbed" hybrids showed only quantitative dif- 

 ferences (that is, lesser quantities than normal hybrids). Schwarze 

 considered that in order for a hybrid substance to appear it must be 

 latent or weakly expressed in one or both parents. As indicated several 

 times in the foregoing chapters, this is not a valid assumption. 



Schwarze attributed increased flavonoid synthesis to inter- 

 actions, generally deleterious in effect, between P. vulgaris cytoplasm 

 (female parent) and P. coccineus nuclear genes. It is true that gen- 

 erally unfavorable conditions bring about increased flavonoid synthesis. 

 Alston (1960) has discussed this point in connection with anthocyanin 

 pigments. One important point which seems to bear on such matters 

 is that stress, broadly defined, must be expected to overcome normal 

 homeostatic mechanisms, resulting in the accumulation of "useless" 

 products— in the particular condition— via side reactions if the enzyme 

 system is available. The stress may be extrinsic (that is, environmental) 

 or intrinsic (that is, genetic or cytoplasmic). Schwarze also supports 

 this hypothesis. If such a result generally occurs, one might expect 

 the accumulation of detectable amounts of substances in hybrids 



