Cells and Tissues 67 



formed of denser portions alternating with more watery layers. 

 In Rice and Oat seeds they are compound. 



2. Sugars, fatty oils, inulin are other forms of non-nitro- 

 genous reserve food. Inulin like sugar is found in solution, 

 but it may be crystallized out by irrigating the tissue with 

 alcohol. It may be found in tubers of certain Composite, 

 e.g. Dahlia, Othonna, in Campanulaceae and other orders. 



Starch, sugar, inulin are like cellulose carbohydrates ; i.e. 

 they consist of the elements carbon, hydrogen, oxygen, in 

 which H and O are combined in the same proportion as in 

 water. 



3. Proteids. Food containing nitrogen may be stored in 

 the form of proteid grains. These are larger and more easily 

 examined in oily than in starchy seeds. In the Castor Oil seed 

 the proteid is especially large. It consists of a proteid body 

 enclosing one or more proteid crystalloids and a mineral 

 granule globoid, made of a double phosphate of calcium and 

 magnesium. While the proteids are distinguished from the 

 oils and carbohydrates as nitrogenous foods they also contain 

 carbon, hydrogen, and oxygen and in addition sulphur and 

 sometimes phosphorus. 



4. Amides are simpler forms of nitrogenous foods con- 

 taining carbon, hydrogen, nitrogen, and oxygen. They occur as 

 reserve food chiefly in roots, bulbs, and tubers as asparagin, 

 tyrosin, and leucin. 



5. Minerals. Crystals of calcium oxalate are frequently 

 found in cells. These are generally regarded as excretions, 

 i.e. when once set apart they no longer function in the plant's 

 activity. Crystals may occur singly or in groups. They are 

 frequently octahedral. In the vine and in many monocoty- 

 ledons they occur as clusters of raphides or needle-shaped 

 crystals. 



Calcium carbonate is more rarely found. It occurs in the 

 form of cystoliths, e.g. fustida, Ficus, Morus. In the develop- 

 ment of cystoliths an ingrowth appears on the wall of an 

 epidermal cell, forming a stalk and an expanded portion, the 

 latter appearing like a cluster of grapes. It diminishes in size, 

 and bubbles of COa are given off when the cystolith is treated 

 5 * 



