166 ELEMENTS OP STRUCTURAL BOTANY. 



277. If starch-granules be subjected to the action of 

 saliva, it will be found that a portion of each granu\e is 

 slowly dissolved out, leaving an insoluble skeleton behind. 

 The granule, therefore, consists of two distinct parts, the 

 more soluble portion being known as granulose, and the 

 less soluble framework as starch-cellulose. 



278. Crystals. These are of common occurrence in 

 many plants, not only in the cell - cavities, but also 

 imbedded in the substance of the cell-wall. They are 

 also of various shapes, and may either occur separately or 

 be massed together in clusters. The needle-shaped forms 

 are known as raphides. These crystals consist for the 

 most part of calcium oxalate, but calcium carbonate 

 is also found, and may be readily distinguished from the 

 former by the effervescence occasioned on the addition of 

 hydrochloric acid. The oxalate dissolves in this acid 

 without effervescence. 



Crystals may be readily observed under the microscope 

 in thin sections of scales from the Onion bulb, Rhubarb, 

 Indian Turnip, and many other plants. 



279. In the leaves of plants of the Nettle Family it 

 frequently happens that a wart-like growth of cellulose 

 takes place on the inside of the cell-wall, the inwardly 

 projecting mass being attached to the wall by a slender 

 stalk, and having multitudes of small crystals imbedded 

 in it. Such inward growths are called cystoliths ; they 

 may be readily seen in cross-sections of the Nettle leaf. 



280. Crystalloids. Seeds, especially those of an 

 oily nature, as they approach maturity and become dry, 

 develope in their cells multitudes of small rounded bodies 

 of an albuminous nature known as aleurone-grains, and 



