310 



BIOCHEMICAL SYSTEMATICS 



It is obvious from these data that the chemical composition of 

 turpentines from the area of overlap did not always match the mor- 

 phological features of the trees from which they were derived. 



An important point stressed by Mirov is what he refers to as 

 "dominance" of the complex terpenes over the simpler phellandrene 

 type. This does not mean strictly Mendehan dominance, merely that 

 more of the pinenes appears than does phellandrene— in the artificial 

 hybrid a 3 : 1 excess. In practically all of the natural hybrids there 

 was 20 to 40 per cent phellandrene. In another example cited by Mirov, 

 dominance of complex terpenes is impHed in Mentha inter-specific hy- 

 brids (from Sievers, et al. 1945). The specific instance which Mirov has 

 in mind must be the cross Mentha arvensis x M. aquatica wherein hy- 

 brids contained 57.6 and 60.8 per cent menthol while the M. arvensis 

 parent yields 65.9 per cent menthol. (Menthol is a saturated mono- 

 hydroxy derivative of phellandrene.) Yet, in the cross, M. arvensis X 

 M. spicata, the menthol content of four plants was respectively 5.3, 

 7.3, 9.8, and 40.5 per cent. This seems contradictory to the point made 

 by Mirov. 



An additional interesting feature of Sievers' work was that in 

 tetraploids of spearmint as well as an allopolyploid of M. arvensis X 

 M. spicata the oil content was very low. A recent paper dealing with 

 chemical changes associated with induced polyploidy (Hanson et al, 

 1959) notes that tannin content of autotetraploids of Lespedeza was 

 higher than the diploid, and allotetroploids had a higher tannin con- 

 tent than either parental species. Rowson (1958) has shown that 

 polyploids in the genera Atropa, Datura, and Hyoscyamus produce 

 more total alkaloids than their diploid counterparts, and Lukovnikova 

 (1961) reported that polyploid potatoes accumulated larger quantities 

 of several classes of components than did normal diploids. A further 

 investigation of the biochemistry of polyploids is needed before any 

 generalizations are permitted. 



A particularly interesting paper on biochemical components 

 of hybrids is that of Pryor and Bryant (1958). These investigators 

 studied oil characters in certain Eucalyptus species and their hybrids. 

 Several of the phenomena discussed previously in this section are en- 

 countered in the Eucalyptus work. The major segment of the study 

 involved a detailed examination of hybrids of Eucalyptus cinerea X 

 E. macarthuri. These plants were derived from seeds collected from 

 two natural hybrids; thus the group represented an Fo generation (it 

 is not clear whether pollination was controlled or whether other trees 

 of the parental types were nearby, but this does not affect the results 

 of the study). The hybrids were about six years old at the time of the 

 analyses. 



