1416 



GUETTARDA 



GUMS 



GUETTARDA (J. E. Guettard, 1715-1786, physician, 

 mineralogist and botanist in France). Rubiaceae. Forty 

 to fifty tropical and subtropical shrubs of both the 

 eastern and western hemispheres, chiefly the latter, 

 two of which are offered for ornament in southern Cali- 

 fornia. 



Leaves opposite or verticillate, ovate or oblong, 

 petiolate or nearly sessile: fls. in axillary more or less 

 forked cymes, sometimes polygamo-dicecious, 49- 

 merous; calyx continued beyond ovary into a cup- 

 shaped or bell-shaped rim; corolla salverform, with 

 long tube and rounded or oblong segms.; stamens 49, 

 inserted in the tube or throat, not exserted; ovary 

 4-9-celled: fr. a thin-fleshed globular or obtusely 

 angled drupe. 



uruguensis, Cham. & Schlecht. Lvs. 2 in. long, half 

 as wide, elliptic-oblong, somewhat pilose above and 

 more or less tomentose beneath; stipules lanceolate- 

 triangular, caducous: corolla-tube M m - or less long, the 

 5 lobes roundish; calyx-limb very short: fr. an oblong 

 3-4-seeded drupe. Cent. Brazil, Uruguay, Argentina; 

 a small tree, with sericeous corolla, and fr. the size of a 

 cherry which is said to.be edible. 



speciosa, Linn. A littoral evergreen tree: Ivs. broadly 

 ovate with an obtuse or cordate base, acute at apex, 

 pubescent beneath, 5-10 in. long: fls. polygamous, 

 white, in long-peduncled cymes that usually arise in 

 the axils of fallen Ivs.; calyx villous; corolla pubescent, 

 \]/z in. or less long and the limb (with obovate segms.) 

 1 in. across: fr. orange, nearly globular, obscurely 

 lobed or angled, said to be edible. Tropics in eastern 

 hemisphere. B.R. 1393. L. H. B. 



GUEVlNA: Gevuina. 



GUICHENOTIA (Antoine Guichenot, French gar- 

 dener, according to some; from Guichen Bay, New 

 Holland, according to others). Sterculiacese. A few 

 tomentose shrubs in extra-tropical Austral., little 

 known in cult, as greenhouse shrubs. Lvs. narrow and 

 entire, revolute, with leafy stipules: fls. small, in simple 

 racemes opposite the Ivs.; petals 5, small and scale-like; 

 stamens 5; ovary 5-celled, the style simple: fr. a short 

 5-valved caps. G. ledifolia, Gay, has several white fls. 

 in the raceme: Ivs. oblong-linear, obtuse: calyx M m - 

 or less long. G. macrdntha, Turcz., has much larger 

 purplish fls. in racemes of 2 or 3. B.M. 4651. J.F. 

 3:279. L.H.B. 



GUILltLMA: Bactris. 



GUIZOTIA (after Guizot, the celebrated historian). 

 Composite. Annual herbs (of about five species) from 

 tropical Africa, one of which has some economic inter- 

 est from its oil-producing seeds. 



The plants have yellow heads, about 2 in. across, with 

 8 broad, 3-toothed rays and a leafy outer involucre. 

 Seeds can be secured by the pound from S. Fla., and 

 they are listed among miscellaneous agricultural seeds 

 in a few of the largest European catalogues. The plant 

 is cult, in India for the oil. 



abyssinica, Cass. (G. oleifera, DC. Verbeslna saliva, 

 Roxbg.). Erect, annual, nearly smooth: Ivs. opposite, 

 lanceolate, clasping, remotely serrate: heads about 

 %in. wide in a dense cyme. B.M. 1017. Doubtfully 

 in cult, horticulturally in Amer. jq- TAYLOR, t 



GUMS AND RESINS. Of the many thousands of 

 vegetable substances falling under the denomination 

 of gums and resins, but a comparatively small number 

 are of such general importance as to warrant mention 

 here. Their economic value depends upon the physical 

 and chemical properties possessed by them and the 

 abundance in which they are produced. A gum, in 

 the ordinary use of the word, is a substance of a more 

 or less sticky nature or which was at one time of a 

 sticky or plastic consistency. The chemist, however, 



restricts the term gum to certain products having very 

 definite properties, classifying other plant exudations 

 according to their properties and grouping them as 

 resins, gum resins, balsams, and the like. A gum in this 

 restricted sense, is a substance which dissolves or softens 

 in cold water, forming a mucilage, or at least a liquid 

 of gelatinous consistency, and when held in a flame 

 only chars with an odor of burnt sugar. It is insoluble 

 in 60 per cent alcohol, oil of turpentine, benzene or 

 fatty oils. A resin, on the other hand, is a lustrous 

 vegetable substance resembling a gum but which neither 

 dissolves nor softens in cold water and which burns 

 with a bright smoky flame, giving off an aromatic odor. 

 It is more or less soluble in alcohol, oil of turpentine, 

 benzene or warm oils. 



Gums are related, chemically, to cellulose and are 

 not secretion products, as was formerly supposed, but 

 are formed directly from the plant tissues by a breaking 

 down of the cells themselves; sometimes this is a per- 

 fectly normal process but very often it may be con- 

 sidered pathological and is the result of bacterial action. 

 Humidity appears to be the principal controlling factor 

 in the production of gum. Volatile or essential oils are 

 secreted by the cells of many plants of widely divergent 

 relationships and are often characteristic of certain 

 families, like those to which belong the mints and the 

 pines. The resins are oxidation products derived from 

 certain of the volatile oils and thus may indirectly be 

 considered products of secretion. Some plants yield 

 only gum, others only resin, while others again may 

 yield both, in which case the gum and resin may come 

 from different parts of the same plant or may be exuded 

 as an emulsion or mixture. In many plants the resins 

 occur dissolved in volatile oil and though exuded in a 

 liquid state soon become solid through the evaporation 

 of more or less of the volatile oil. Some resins contain 

 aromatic acids and others consist of certain liquid 

 organic compounds of these acids in which is dissolved 

 a solid resin; such products are called balsams. The 

 camphors constitute another group of oxidation prod- 

 ucts derived from the volatile oils. 



Uses of gums and resins. 



Soluble gums, the most typical of which is gum 

 arable, are used for a great number of purposes in the 

 arts; the varieties having the least color, highest 

 adhesive power and viscosity being the most valuable. 

 They find application in confectionery and pharmacy, 

 in sizing and finishing textile fabrics and paper, in 

 calico printing and dyeing, and in the manufacture of 

 fine water-colors, ink, mucilage, and so on. The gums 

 which are more or less insoluble in water, but which 

 swell with it to form a mucilage, as for example traga- 

 canth, are used as thickening agents in calico-printing 

 and in pharmacy, and for pastes, pills and colored 

 crayons. 



Resins are applied to a great variety of industrial 

 purposes but probably the most important of these is 

 the manufacture of varnishes and lacquers. For this 

 purpose they may be roughly divided into two classes: 



(1) those which after melting can be combined with 

 Unseed oil and turpentine to form an "oil varnish," and 



(2) those which dissolve more or less in alcohol, oil of 

 turpentine or other volatile solvents to form "spirit 

 varnishes." The important resins of the first class are 

 amber and the copals; while those of the second class 

 include rosin or colophony, benzoin, dammar, sandarac, 

 mastic and elemi. Aside from varnish-making, certain 

 resins are employed in medicine and pharmacy, for in- 

 cense, and in the manufacture of soap, and the like. 



The gums and resins of greatest economic importance. 



The following list of the plant exudations which are 

 of the greatest economic importance and which com- 

 prises one or more typical examples of each of the 

 groups already mentioned may be arranged as follows: 



