3 o SCIENTIFIC AGRICULTURE. 



55. The elements heretofore mentioned as form- 

 ing the material of plants are sometimes called ulti- 

 mate elements, because they are the simplest forms 

 of matter into which plants can be separated, or re- 

 solved. What are called the proximate elements, 

 or principles, are compound substances, such as 

 starch, sugar, gum, oil, cellulose, or woody fibre, etc. 

 While there are a large number of these, each spe- 

 cies of plant having its peculiar principle, the 

 greater number can be included under the follow- 

 ing groups. 



56. Amylaceous and saccharine substances, 

 such as starch, sugar, cellulose, or woody fibre, and 

 gum. These are composed of only three elements, 

 carbon, hydrogen, and oxygen. The woody fibre, or 

 cellulose, forms the greater part of many plants, and 

 usually consists of small tubes sticking to each other. 

 Cotton fibre is nearly pure cellulose. It is contained 

 in all plants, in the stems, leaves, roots, and seeds. 

 It has the same elements in the same proportion 

 as starch, and differs in these respects very slightly 

 from sugar. It can be converted into one kind of 

 sugar, glucose, by boiling with dilute sulphuric 

 acid. 



57. Pectose substances, like the jellies and 

 pulp of fruits, and of some roots, as the turnip, beet, 

 and onion. These substances are closely related to 

 woody fibre, and are easily changed into it by the 

 plant. 



58. Vegetable acids, such as tartaric acid found 



