90 SUMMAEY OF CURRENT RESEARCHES RELATING TO 



Formation of Gum-arabic* — Herr G. Kraus has determined, by 

 observations on the exudation of gum from Acacia melanoxylon, that 

 it is formed only in the bark, and not in the wood, and only in the 

 bast-layer, never in the parenchyma nor in any more external portion ; 

 that the bast-fibres have no share in its formation ; that it flows from 

 the cells of the soft bast, and especially from the sieve-tubes ; and 

 that it is not a product of degradation of the cellulose, but is a 

 true cell-content, flowing out unchanged through the unchanged cell- 

 walls. 



Oxalic Acid in Plants.j — MM. Berthelot and Andre, to extract 

 this substance, bruise the plant in a mortar, boil with water for one 

 hour, allow to macerate for twenty-four hours, and decant off and 

 filter the liquid. The residue is again extracted with warm water, 

 and finally pressed. If it is required to extract the insoluble oxalates, 

 the water used for maceration must be mixed with 20-30 c.cm. of 

 strong hydrochloric acid for each 100 grm. of plant. The mixed 

 filtrates are acidified with hydrochloric acid (if this has not been 

 already added), boiled, and again filtered. The filtrate is made 

 alkaline with ammonia, and mixed with an excess of boric acid 

 solution, which, in presence of ammonium chloride, prevents the pre- 

 cipitation of nitrates, racemates, citrates, &c., or redissolves these 

 precipitates if already formed. The liquid is then strongly acidified 

 with acetic acid, mixed with calcium acetate, heated below the boiling 

 point for about an hour, and the impure calcium oxalate collected 

 and washed. The precipitate is redissolved in hydrochloric acid, 

 and again collected. This treatment is repeated if necessary, and the 

 purified precipitate is finally weighed as such, converted into calcium 

 sulphate, or treated with a large excess of sulphuric acid and the 

 evolved carbonic oxide measured. 



The paper concludes with some determination of the proportions 

 of soluble and insoluble oxalates in different parts of Chenopodium 

 quinoa, Amaranthus caudaius, Mesembryanthemum crystallinum, and 

 Bumex Acetosa. 



Growth and Increase of Crystals in Plants.^ — According to 

 Herr Otto Kopert, who has examined with this view a considerable 

 number of plants, the relative number of crystals of calcium oxalate 

 in different parts of the stem of plants, and in leaves of different ages, 

 varies with the species. With regard to their size the results are 

 more uniform. They are wanting in the youngest rudiments of 

 leaves, but appear in them in the leaf-bud before they are capable of 

 assimilation, immediately beneath the cone of growth, and attain their 

 maximum size as soon as the organ — root, stem, or leaf — has attained 

 is full development. 



Sphgerocrystals of Calcium Oxalate in the Cactace3e.§ — In 

 addition to the well-known crystals of calcium oxalate of various 



* Ber. Sitz. Naturf. Gesell. Halle, 1884, pp. 19-20. 



t Comptes Eendus, ci. (1885) pp. 354-60. 



t Zeltschr. f. Naturwlss., Iviii. (1885) p. 140. 



§ Ber. Deutscb. Bot. Gesell., iii. (1885) pp. 178-82 (1 fig.). 



