84 THE PLANT CELL. 



1« Crystals occurring in certain cells, 



2. Crystalloids. 



3. Cystoliths. 



1. Crystals of oxalate of lime, Ca(C02)2, may occur in the 

 following forms : — 



«• Raphides, or elongated aoioular crystals, found singly or in sheaves 

 in the cells of the cortex in the stem of Draanna (see Fig. 67). They also 

 occur in the root of Hyacinthus and many other plants. 



/3. Quadratic crystals occurring singly in cells of the leaf of Begonia. 



y- Clustered crystals, also occurring in leaf-cells of Begonia, and in 

 other tissues (see Fig. 68). 



These crystals are distinguished from those of other salts by 

 the fact that, on addition of dilute hydrochloric acid, they dissolve 

 without effervescence, whilst they are insoluble in acetic acid. 



Oxalic acid is a bye-product of metabolism in the cell, and it 

 combines with calcium to form calcium oxalate, which separates 

 out, in this case, in the living cell.* 



Fig. 69.— A Cystolith of Carbonate of Lime (CaCOj) foemed in an 

 Epidermal Cell of the Leaf of Ficus elastica. Note the "core" 

 of cellulose upon which numerous layers of carbonate of lime are 

 deposited. 



2. Crystalloids, or, as they are often called, spheroids, of a 

 substance known as iuulin (a carbohydrate), separate out in the 

 cells of the tubers or petiole of Dahlia when these are treated with 

 alcohol. Inulin takes the place of starch or sugar in these cells. 

 The spheroids have a peculiar concentric and radiating structure 

 (see Fig. 71, a) which is very characteristic. Large spheroids of 



* Occasionally crystals of oxalate of lime are found in the walls of cells 

 (mesophyll cells of Wellingtonia). 



