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CHAPTER IV. 



OF THE ORGANIC SUBSTANCE OF PLANTS. 



Structure of the Roots, Stem and Leaves. Course of the sap. 

 Composition and properties of water. Great number of organic 

 bodies. Woody fibre, Starch, Sugar, Gums. Composition of 

 these bodies and their mutual relations. Organic substances 

 containing Nitrogen. Sources of organic elements: Carbon, 

 Carbonic acid, Hydrogen, Oxygen, Nitrogen. 



SECTION I. STRUCTURE AND FUNCTIONS OF THE PLANT IN 

 ITS SEVERAL PARTS. 



The different external parts of plants are well 

 known, they consist of roots, stems, bark or epider 

 mis, and leaves. 



The internal structure and the functions of the roots 

 are not so perfectly understood as that of the other 

 parts, owing to the difficulty of knowing exactly what 

 occurs underground. At a short distance beneath the 

 surface they begin to divide, sending out little rootlets 

 in every direction, and at the extreme end of each is 

 a small bundle of soft, minute, white fibres. These 

 are all so many mouths for the nourishment of the 

 stem. If you place the roots of a growing tree in 

 certain colored liquids, its body will soon become 

 colored. This part of the plant has, to a considerable 

 extent at least, a power of selection, as it is found 

 that certain substances are admitted to the exclusion, 

 either partial or total, of others. Some coloring solu 

 tions for instance, as above, enter with facility and 

 tinge the whole stem in a short time, while others are 

 scarcely absorbed at all. The same must, in a degree, 



