24] 



CHAPTER I. THE CELL. 



sisting of double phosphate of lime and magnesia ; lessjrequently 

 there is a crystal, or a cluster of crystals, of calcium oxalate. 



In the large grains of oily seeds it is frequently the case that a 

 portion of the proteid (globulin) of the grain crystallises out, con- 

 stituting the crystalloid ; there are occasionally two or more 

 crystalloids in the grain (Fig. 54). 



8. Mineral Crystals are frequently found in the cells of plants. 

 They sometimes consist, but in comparatively few cases, of calcium 

 carbonate ; for example, the crystals in the protoplasm of Myxo- 

 mycetes, and the crystalline masses occurring in the cells of the 



FIG. 64. Cells from the endosperm 

 of Bicinii* communia (x 800) : A fresh, 

 in thick glycerine ; B in dilute gly- 

 cerine ; C warmed in glycerine ; D after 

 treatment with alcohol and iodine ; the 

 grains having been destroyed by sul- 

 phuric acid, the cytoplasm remaining 

 behind as a net-work. In the grains 

 the globoid may be recognised, and in 

 B C the crystalloid. (After Sachs.) 



Fie. 55. Cells of a very thin section through 

 a cotyledon of the embryo in a ripe seed of 

 Pisum sativum ; the large concentrically strati- 

 fied grains St are starch-grains (cut through) ; 

 the small granules a are aleuron, consisting 

 of proteids ; i the intercellular spaces. (After 

 Sachs.) 



pericarp and testa of some plants (e.g. Celtis australis, Litlio- 

 spcrmwn officinale, Cerinthe glabra). 



In all other cases the crystals consist of calcium oxalate, which 

 crystallises in two systems according to the proportion of water 

 which it contains ; to the one system, the quadratic, belong the 

 octahedra (Fig. 57 fc) ; to the other, the clinorhombic, belong the 

 acicular crystals, distinguished as raphides, which occur in 

 bundles in the cells of Monocotyledons more especially (Fig. 58), 

 and are generally associated with mucilage in the cell. 



M.B. G 



