7O JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS unusually sweet-tasting form of the gum exuded from the main trunk of the trees (gum is normally exuded from the upper branches)--were also studied. Table III shows the results for the tapped, bulk, samples from Qala en Nahal, Kassala Province (heavy clay soil, QN 1-5) from Umm Ruaba, Kordofan Province (sandy soil, UR 1, 2) and from Goz el Ganzara, Kordofan Province (sandy soil, GG 1-5). Table IV shows the results for the single-nodule, natural exudate, samples. Consideration of these results shows Table IV Analytical data for single-nodule natural exudate Acacia senegal gum Sample Age of Crude material Electrodialysed material tree Moisture Ash Nitrogen (oc)D Limiting-viscosity (¾) % % % (degrees) number (cm 3g-l) A1 25 12.6 3.72 0.24 --29 12.5 334 000 A2 11.6 3.78 0.23 --31 11.6 291 000 A3 11.1 3.80 0.24 --32 11.0 264 000 B1 12 11.7 4.43 0.23 --28 15.6 504 000 B2 12.9 4.44 0.23 --29 15.8 516 000 C1 8 10.4 3.40 0.27 ---29 11.0 264 000 C2 9.8 3.66 0.26 --31 11.0 264 000 D 15 15.6 3.88 0.32 --30 14.1 418 000 E 12 12.8 4.64 0.34 --32 14.5 440 000 F 17 13.3 4.01 0.35 --29 15.1 474 000 G 20 15.4 4.15 0.23 --31 12.2 320 000 H 10 14.7 3.97 0.45 --29 14.4 434 000 I 15 12.1 3.27 0.33 --27 15.0 468 000 Average 12.6 3.93 0.29 --30 13.4 Range 9.8 3.27 0.23 --27 11.0 15.6 4.64 0.45 --32 15.8 Standard deviation 1.8 0.40 0.06 1.5 1.9 *From [q]=K' Maw' where K'=I.3x 10-2 and a=0.54 Reproduced from Carbohydrate Research, 6 97 (1968) that the variations are similar in extent to those observed for the other Acacia spp. studied. Furthermore, in agreement with the results for A. laeta gum (32) the three nodules from tree A are closely alike the same effect was shown by the two nodules from tree B, and by the two nodules from tree C. In the genus Acacia the gum exudates are clearly characteristic of a particular tree of that species. Variation within species must therefore be expected when all the factors are taken into consideration--seasonal, soil, age of tree, nature of the injury stimulating gum flow, etc.--it is surprising that the extent of the variation in chemical and physical properties of such a complex natural product is not indeed greater than has been revealed in these studies. There is evidence, however, that certain genera, e.g. Acacia, Lannea (37) and Araucaria (38) are not, in relative botanical terms, par-

RECENT ADVANCES IN THE CHEMISTRY OF ACACIA GUMS 71 ticularly variable other genera (e.g. Combretum) are very much more complex and variable, and this is reflected in the composition and properties of their gum exudates ($0). 36 T• 28 GG2 HW QNI BB(•:) S'S (a) • BI ',B2 BB(b) AI D E H G A2 A3 el C2 o 0.008 O.Oi 6 0.024 0.032 C,g ml-I Figure Table V shows the comparative analytical data obtained for some typical and atypical specimens of A. senegal gum. More fundamental structural studies of these specimens were undertaken (40): these showed that the beetle-borer specimen was virtually identical to "normal" exudate gum the "Hennawi" variant was basically similar, but differed in two important aspects concerning some of the peripheral end-group positions involving the rhamnose and glucuronic acid residues. Theories of the origin, function, precursors, and the mode of biosynthesis of gum exudates were therefore examined critically in terms of these results. In particular, two of the theories that have been proposed in the past must be seriously questioned. (a) The enzyme systems that would be necessary to transform starch (a polyglucan) into a highly branched heteropolymer of galactose, arabinose, rhamnose, glucuronic acid, and 4-o-methylglucuronic acid appear to be im- possibly complex and the mobilisation of hemicellulosic-type arabino- galactans by enzymic modification would be a much more simple bio- synthetic route. (b) Since the composition, properties, and structure of the exudate from A. senegal appears to be independent of the nature of the