CHEMISTRY OF PLANTS. 



3. 



tigated. It appears to be present in 

 every plant, and in some in very large 

 quantities. A stem of Cereus senilis, 

 after the water was driven off, con- 

 tained eight hundred and fifty-five 

 parts oxalate of lime in the thousand. 

 The form of the crystal of oxalate of 

 lime is the quadratic octaedron (fig. 

 1.); and it presents, like almost all compounds of the earths, as its 

 primary form, the right-angled four-sided prism (in the binaxial and 



unaxial systems). The following forms 

 are easily distinguished : * 1. Needle- 

 formed crystals (Raphides, DeCand.\ 

 being a combination of a very long 

 prism with an octaedron (fig. 3. b\ 

 whose surface, as in the Zircon and the 

 Hyacinth, is united with the surface 

 of the prism. These lie together in 

 bundles of from twenty to thirty in 

 a single cell, which they entirely fill 

 up; and are present in almost all 

 plants, and may be well seen in 

 Phytolacca decandra (fig. 3. c). 



2. Large single crystals, either of the form of the last 

 (fig. 3. a), and then very long, as in the Agave americana, or 

 the primary forms or combinations, are octaedrons of the first 

 or second order, with two or three blunt or pointed. This 

 last form is seen very beautifully in the pollen of many species 

 of Caladium, and in the parenchyma of the old stems of 

 Tradescantia (fig. 2.). 



3. Large crystals, in which the crystals have developed 

 one upon another, or grown to organic cells in such a way 

 that they constitute irregular-formed glands. They are so 

 common amongst phanerogamous plants at one season of the 



year or another, that it would be difficult to give an example of a 



plant in which they do not exist. They 

 are easily observed in the Cactacccc. 



Next to oxalic acid with lime, car- 

 bonic acid is most frequently found, 

 and this in combination with lime. 

 The carbonate of lime assumes a va- 

 riety of forms, but most commonly that 

 of the pure rhomboedron (fig. 4.) ; as, 



for instance, in the Cycadacece, in many Cactacefe, and in the leaves of 



species of Costus. 



Sulphate of lime is also found, in the form of single or double 



octaeclrons, or in a tabular form, as octaedrons above and below, with 



* Even through artificial precipitation, oxalate of lime is never amorphous, but is 

 constantly crystallised, as shown by Valentin, Repertorium, vol. ii. p. 30. 



2 Oxalate of lime as a quadratic octaedron, and a combination of three octaedrons, 

 found in the pollen of a species of Caladium. 



* a, Quadratic pillars combined with octaedrons. b, The same elongated. c, A 

 bundle in a cell. 



4 Carbonate of lime, as seen in the epidermis of Cactncefe. 



