598 Transactions of the Society. 



&c, but they are distinguished by their solubility in water, or in 

 acetic acid. All plant -crystals which are insoluble in water and 

 acetic acid, and soluble in mineral acids, are composed of calcium 

 oxalate. 



There are no crystals of calcium carbonate or sulphate in 

 plants.* 



Holzner has given a table for distinguishing the crystalline 

 formations in plants by chemical reactions.! 



II. Crystalline .form of Calcium oxalate. — Calcium oxalate 

 crystallizes in the tetragonal system, with three molecules of 

 water ; in the monoclinic system, with one molecule of crystalliza- 

 tion water. The octahedrons are generally tetragonal (e. g. crystals 

 of Begonia, Tradescantia, &c); the short prismatic crystals, the 

 raphides, and all those crystals which were believed to be of sul- 

 phate of calcium (e. g. the long prismatic crystals of Iris), are mono- 

 clinic. 



III. Forms of Plant-crystals. — The various forms of plant- 

 crystals have been described by Gulliver, who distinguished four 

 principal forms : raphides, sphas raphides (drusen of the Germans), 

 short prismatic crystals, and long prismatic crystals. 



The raphides have been the principal object of Gulliver's 

 researches. They are frequent in Monocotyledons, and are found 

 also in some families of Dicotyledons. Gulliver has described 

 them in Vitaceae, BalsaminaceEe, Galiaceae, and Onagracese, and in 

 numerous other orders of plants, but in the British Exogens so 

 confined to the last three orders as to be characteristic of them ; 

 Hydrangea, by its raphides, he finds sharply distinguished from 

 the Saxifragacese, under which order it is usually placed; and 

 Montinia by its want of raphides as plainly differing from its 

 assigned order, Onagracese.:]: 



The other crystals may be found free and abounding in the 

 cavities of plant-cells, or one in every cell. The little prismatic, or 

 tabular crystals, and the simple octahedrons, which are in many 

 Gesneriaceae, Bignoniacese, Scrophularineee and Labiatse, belong to 

 the first case. To this also belongs, I think, the crystalline powder 

 of Sambucus and of many Solanacese. To the second case belongs 

 the greatest number of plant-crystals, especially those which are 

 grouped in druses (very common in the pith and bark of ligneous 

 plants) and the short prismatic crystals of the bast-cells. 



* But see Beale's ' How to work with the Microscope,' 5th ed. p. 174, p]ate 

 xlvii. for Gulliver's description and figures of sphseraphides of carbonate of 

 lime. — Ed. 



f See " Bern erkun gen zum Referate iiber Gulliver's Liste krystallhaltiger 

 Bflanzen," von Prof. Dr. Georg Holzner, Zeitschr. f. Mikrosk., i. (1877), Heft 2, 

 pp. 42-44. 



J ^ee this Journal, iii. (1880) p. 44 ; and Quart. Journ. Micr. Sci., 1866, and 

 on Pollen, &c, in Pop. Sci. Beview, 1868. 



