SACS CONTAINING CRYSTALS. 14I 



wall of the sac is often strongly thickened, especially in Citrus, where the crystal 

 appears inserted in the very thick lateral wall, or in a conical excrescence of it. In 

 the septate sacs of the wood of Herminiera elaphroxylon ^ there lies in each of the 

 almost cubical segments one klinorhombic plate, with one side fitted into the strongly 

 thickened inner wall of the sac, while the rest almost fills the cavity of the segment. 

 I could not in this case find a membrane surrounding the crystal. The space not 

 occupied by the crystal in all these sacs is in the mature state apparently filled with 

 water. 



Many crystals of whatever form, with the exception of Raphides, appear to lie 

 free within the membrane of the sac, being either closely surrounded by it, but 

 without attachment, or suspended in an apparently watery fluid. Thus, e. g. the large 

 crystals of Iris, and the crystalline granules. For all these cases, however, it remains 

 to be more definitely determined whether a gelatinous coat or an attachment to the 

 wall is present or not. The general occurrence of such a condition is attested by 

 Payen in his statements on the occurrence of silicious coats round grouped crystals, 

 and of membranous sheathing layers of a granular substance which turns brown with 

 iodine. Compare Hofmeister, Pflanzenzelle, p. 393. 



Crystal-containing sacs occur in all parts, and in all tissues of plants ; they appear 

 most abundantly, and often in very great quantity [the stem of Cereus senilis contains 

 in the dry substance more than eighty-five per cent, of calcium oxalate (Schleiden)], 

 in the parenchyma of sappy foliage, and in leathery leaves, bordering closely on the 

 vascular bundles, and arranged in rows which follow these, in the bast and pith of 

 dicotyledonous plants, often also in the secondary xylem-parenchyma(Pterocar' us 

 santalinus, Hsematoxylon, &c.), and in the medullary rays of the wood (e. g. Camellia 

 japonica, Vitis ; compare Chapter XIV) : where large air-containing intercellular 

 spaces are present they are often particularly numerous at the limits of these, and 

 project into them : e. g. Aroidese, Pistia, Myriophyllum. 



They occur in most families, and usually in all genera and species of a family : 

 jn those in which regular crystal-bearing sacs are rare, or absent, the calcium oxalate 

 is often deposited in the form of small crystals in the contents of parenchymatous 

 cells,, or, as in the Cupressineae, Taxinese, Ephedra, and Welwitschia ^ in the cell- 

 membranes. 



The more generally this rule applies the more worthy of attention is a series of 

 exceptions. In the Equiseta no oxalate of lime is observed anatomically. The same 

 is the case in most Ferns, Graminese, and the Potameae (with the exception in the 

 Phanerogams of the parts of the flower). Still exceptions occur in many of the above 

 families : such as crystals in the Epidermal cells of Asplenium Nidus, in the covering 

 plates of the Cyatheaceae (comp. p. 128), numerous clusters of crystals in the 

 parenchyma of the stem of Panicum turgidum. 



On the other hand, crystal-containing sacs, or crystals, are not found at all in 

 certain species or genera of families, the members of which, as a rule, contain 

 them in large quantity. In Nicandra physaloides and Petunia nyctaginiflora I found 

 no crystal-containing sacs, while the rest of the Solanaceae, which have been in- 



' Hallier (Botan. Zeitg. 1864, Taf, III) gives the outline of these cells correctly, but with a 

 wrong description. 



• ■^ Compare Graf zu Solms-Laubach, Botan. Zeitg. 1871. 



