MINERAL FOOD OF PLANTS. CELLULOSE. 67 



corrode glass, is detected in the ashes of some plants. It 

 occurs in combination, as fluoride of calcium, or fluor 

 spar, in which form it is also found in the teeth and bones 

 of animals. 



All these earthy substances are called the mineral food 

 of plants. 



UNI VK ^I.T 



CHAPTER VIII. ( A1 



ORGANIC COMPOUNDS IN PLANTS. 



239. Of the simple, elementary substances spoken of in 

 the last chapter, and their direct compounds, although they 

 are all found in plants, none ever appear in particles large 

 enough to be seen by the naked eye. Of them, however, 

 are formed the substance and the nutritious and other 

 useful products of the plants, called the organic com 

 pounds. 



240. They are so called, because they are compounds 

 formed by the action of the vital power of the organized 

 being, a plant. 



241. Among the most important are, first, those formed 

 of carbon, oxygen and hydrogen only, viz., Cellulose, 

 Vegetable Jelly, Starch, Gum, Sugar, and Oil. 



242. Cellulose, also called woody fibre, is the cell-mem 

 brane, or thin covering of the cells. When first formed, it 

 is tender, flexible and elastic, clear and transparent. It is 

 expanded by moisture and contracted by drying. It is 

 permeable to all fluids, which enter on one side and pass 

 out on the other. It is called woody fibre, because it 



