PART I. 



THE CHEMICAL PROCESSES IN THE NUTRITION OF 

 VEGETABLES. 



CHAPTER I. 



The Constituent Elements of Plants. 



Carbon and hydrogen invariably occur in all parts of plants. 

 They form constituents of all their organs, and are essential to 

 their existence. » 



The substances which constitute the principal mass of every 

 vegetable are compounds of carbon with oxygen and hydrogen, 

 in the proper relative proportions for forming water. Woody 

 fibre, starch, sugar, and gum, for example, are such compounds 

 of carbon with the elements of water. In another class of sub- 

 stances containing carbon as an element, oxygen and hydrogen 

 are again present ; but the proportion of oxygen is greater than 

 would be required for producing water by union with the hydro- 

 gen. The numerous organic acids met with in plants, belong, 

 with few exceptions, to this class. 



A third class of vegetable compounds contains carbon and hy- 

 drogen, but no oxygen, or less of that element than would be 

 required to convert all the hydrogen into water. These may be 

 regarded as compounds of carbon with the elements of water, and 

 an excess of hydrogen. Such are the volatile and fixed oils, 

 wax, and the resins. Many of them have acid characters. 



The juices of all vegetables contain organic acids, generally 

 combined with the inorganic bases, or metallic oxides ; for metal- 

 lic oxides exist in every plant, and may be detected in its ashes 

 after incineration. 



