Search

The genus Gentiana, composed of over eight hundred species is world -wide in its distribution members being found in Europe, Asia, Africa, Australia, New Zealand and North and South America. The continent of Asia seems to be the centre of distribution as here the greatest number of species is found, the majority being described from Western China and the adjoining states. As a genus it is by no means confined to any one habitat as species may be found on high alps, on screes, in woodland, in meadows, in marshes and even in peat bogs. As the flowers show considerable variation in colour and as many of the species are highly suitable for cultivation the genus has become one of horticultural importance. While the genus has proved a fairly popular subject with systematists there has been very little investigation on its anatomical aspect. The most extensive work has been by E.Perrot in his "Anatomie comparée des Gentianacées" (1).As in this work he has been investigating the anatomy of the family as a whole, he has not given much detail on the anatomy of the genus Gentiana, especially on their roots and leaves, and therefore it is these structures which have formed the basis for this investigation. The species investigated were obtained from plants growing in the Royal Botanic Garden, Edinburgh and only those were studied where the specific name had been definitely confirmed. These species were: - G.a.caulis. Linn || G.Loderi. Hook.f. || G.Andrewsii. Griseb. || G. X Macaulayi. || G.angulosa. Bleb. || G.macrophylla. Pall. || G.angustifolia. Vill || G.Makinoi. Kusnezow. || G.asclepiadea. Linn || G.Newberryi. A.Gray. || G.bellidifolia. Hook.f. || G. cachem.irica . Decne || G.cephalantha. Franch. || G.corymbifera. T.Kirk. || G.crassicaulis. Duthie. || G.cruciata. Linn. || G.dahurica. Fisch. || G.decumbens. Linn || G.depressa. D.Don. || G.Farreri. Balf. .f . || G.Fetisowi. Regel & Winkler. || G.ornata. Wall. || G.Parrvi. Engelm. || G.phlogifolia. Schott & Kotschy. || G.Pneumonanthe. Linn. || G.prolata. Balf.f. || G.purpurea. Linn. || G.saxosa. Forst.f. || G.scabra. Bunge.var. Buergeri. Maxim. || G.sceptrum. Griseb. || G. septeli:fida. Pall. || G.setigera. A.Gray || G.gilvostriata.Marquand. || G.sino-ornata. Balf.f. || G.gracilipes. Turrill || G.stragulata. Balf.f. & Forrest. || G.Grombczewskii.Kusnezow. || G.straminea. Maxim. || G.hexaphylla. Maxim. || G.tianschanica. Rupr. || G.hexaphylla x Farreri. || G.trichotoma. Kusnezow. || G.Kochiana.Perr.& Song. G. || Veitchiorum. Hemsl. || G.Kurroo. Royle. || G.verna. Linn. || G.lagodechiana.Kusnezow.

This thesis describes an investigation of 2:6-dihydroxy benzoic acid and its salts by X-ray analysis. The unit cell dimensions of 2:6-dihydroxy benzoic acid monohydrate have been obtained and the possible space group is discussed. The main part of the work is concerned with the crystal and molecular structure of the potassium and rubidium salts of 2:6-dihydroxy benzoic acid and a complete structure analysis of the potassium salt has been carried out. The crystals of 2:6-dihydroxy benzoic acid monohydrate are orthorhombic, space group Pna2 1 (C9 20) or Pnma (D 16 2h) with 4 molecules per unit cell. The unit cell dimensions are a = 6.77. b = 9.67 and c = 11.92 A. Potassium 2:6-dihydroxy benzoate crystallises in the monoclinic space group P2 1/n (C5 2h) with four molecules per unit cell. The unit cell dimensions are a = 3.94, b = 15.10 and c = 13.37 A. beta = 99 11' The structure of the compound has been elucidated by the Isomorphous Replacement method, in which use was made of the isomorphous rubidium salt. Refinement proceeded from a study of Fourier syntheses in all three zones and Fourier difference syntheses projecting on (100). Electron density projections on the (100) plane gave good resolution of all the atoms in the asymmetric unit. The shortness of the a axis prevented good resolution in the h01 and hk0 zones and the x co-ordinates were obtained largely by trial and error methods after an approximate x co-ordinate for the potassium ion had been obtained from a study of the far-out reflections in the hk0 and h01 zones. However, from the electron density projections, x co-ordinates could be assigned to the potassium ion and most of the oxygen atoms. The co-ordinate standard deviations are less than .02 A. The molecule is planar within experimental error and bond lengths vary between 2.75 and 3.03 A for potassiura-oxygen bonds, between 1.25 and 1.40 A for carbon-oxygen bonds and between 1.39 and 1.53 A for carbon-carbon bonds. There are two intramolecular hydrogen bonds joining the oxygen atoms of the carboxyl group to the phenolic oxygens; these are 2.50 and 2.56 A in length. There are no discrete molecules and the packing is determined by the co-ordination of the organic residues to a central metal ion by potassium-oxygen links in all directions, involving both phenolic and carboxylic oxygens. The potassium is surrounded by seven bonded oxygens, six of which are arranged to form a trigonal prism. The ion shows a preferential attraction to one of the two oxygen atoms of the carboxyl group and has an attraction of similar magnitude to both of the phenolic oxygens. The bond lengths within the organic residue are reasonably consistent with Cochran's values for salicylic acid. It is expected that the work on the potassium salt will shortly be published.