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A TEXTBOOK OF THEORETICAL BOTANY 



Crystals are also of frequent occurrence in cells (Fig. 467). The principal 

 substance which forms these crystals is Calcium oxalate. It may form 

 large, solitary rhombohedra or crystals twinned in various ways. One 

 frequent type is the cluster crystal, a spherical aggregate with points radiating 



I 



Fig. 467. — Types of cell crystals of Calcium oxalate : A, Carica papaya. Cluster crystal in 

 cortical cell. Byjfuglatis nigra. Cluster crystal with organic centre in phloem parenchyma. 

 C, Viburnum lentago. Cluster crystal in cortical cell. D, Carya glabra. Cluster crystal 

 embedded in stone cell. E, Smilacina racemosa. Bundle of raphides in pulp cell of fruit. 

 F, Jiiglans nigra. Rhombohedral crystals in wood parenchyma. G, Tilia americana. 

 Rhombohedral crystal in phloem parenchyma. Types of reserve substances : H, 

 Fragaria sp. Starch grains in pith cells. J, Pisum sativum. Compound grains in cell of 

 cotyledon characteristic of wrinkled seeds. K, Ahophila sp. Starch grains in pith cells. 

 L, Phajus grandiflorus. Formation of starch grain in plastid. M, Dahlia variabilis. 

 Sphaero crystals of inulin. N, Solanum tuberosum. Starch grains in underground stem. 

 Eccentric type. O, Triticum vulgare. Starch grain in endosperm. Centric type. 

 P, Phaseolus multiflorus. Starch grains in cotyledon. R, Ricinus communis. Aleurone 



grains in endosperm. (From various sources.) 



out all round it. Another form, commonest in Monocotyledons, consists of a 

 sheaf of fine needles, which are called raphides. 



In the leaves of the Urticaceae and their allies there often occur certain 

 enlarged cells, called idioblasts, in which crystalline aggregates of Calcium 

 carbonate are deposited on a cellulose peg, which projects from the cell 

 wall. These cystoliths may fill the whole cell (Fig. 468). 



