244 BIOCHEMICAL SYSTEMATICS 



investigations pertaining to enzymatic interconversion. In the fruit 

 juice of Lagenaria siceraria an enzyme catalyzes efficiently the con- 

 version of E to B while the reverse reaction occurs more slowly. 

 The authors conclude that A is formed from B, and C from B. 

 Enzymes occur which convert E to I, B to D, and C to F. All of these 

 conversions involve loss of a two-carbon group. Surprisingly, the 

 highest activity for this type of conversion is found in the fruit juice 

 of a non-bitter Golden Hubbard squash. An alternate pathway to 

 cucurbitacin D, from F, occurs apparently in leaves and fruits of 

 Cucumis angolensis. 



Emslin and Rehm summarize their evaluation of the taxo- 

 nomic significance of the cucurbitacins in a brief paragraph, as 

 follows: 



The main conclusion emerging from this study of the biogenetic inter- 

 conversions is that there are only two primary bitter principles, which 

 are chemically very labile, and easily transformed to other related sub- 

 stances by enzyme systems present both in bitter and non-bitter 

 plants. It is therefore not surprising that a knowledge of the bitter 

 principle composition of species appears to be of little value to the 

 taxonomist. 



The authors then go on to note distinctions between Cucumis 

 and Citrullus as follows. All species of Cucumus investigated con- 

 tained cucurbitacin B while Citrullus species contained only E in their 

 seedling roots. In Cucumis the cucurbitacins occur mainly as agly- 

 cones while in Citrullus they occur as glycosides. Possibly the authors 

 are unduly pessimistic regarding the systematic significance of these 

 substances. Since they state that an effective paper chromatographic 

 method is available for their study, it is likely that intensive studies 

 of populations, particularly natural populations, would prove useful. 

 It is not likely that cultivated varieties would offer as much promise, 

 considering the labihty of the group, as would wild species. 



Another phytosystematic investigation of higher terpenes is 

 that of Hollo way (1958) who studied the diterpenes of the phyllo- 

 cladene and podocarprene types. Among the former group several 

 diterpenes, phyllocladene, rimuene, mirene, and kaurene are closely 

 related and possibly isomers. The podocarprene group is chemically 

 similar, and representatives of both types occur together in at least one 

 genus, Sciadopitys. With the exception of Sciadopitys these diter- 

 penes are confined to the tribes Araucarineae or Podocarpineae. 

 Diterpenes of other types occur in other conifers, for example, in 

 Pinus. Since, in older classifications the order Coniferales was divided 

 into two families, the Pinaceae (including Araucaria and Sciadopitys) 



