1 08 ORGANIC CONSTITUENTS OF PLANTS. 



given to cattle, or laid up for preservation, and dried at 230 Fahren- 

 heit; the organic matter being indicated by the carbon, oxygen, 

 hydrogen, and nitrogen ; the inorganic by the ash : 



Wheat. Oats. Peas. Hay. Turnips. Potatoes. 



Carbon 455 507 465 458 429 441 



Hydrogen, 57 64 61 50 56 58 



Oxygen, 430 367 401 387 422 439 



Nitrogen, 35 22 42 15 17 12 



Ash, 23 40 31 90 76 50 



By the process of drying, the 1000 parts of these substances lost water 

 in the following proportions : 



Wheat, 166 Peas, 86 Turnips, 925 



Oats, 151 Hay, 158 . Potatoes, 722 



211. As plants have no power of locomotion, it follows that their 

 food must be universally distributed. The atmosphere and the soil 

 accordingly contain all the materials requisite for their nutrition. 

 These materials must be supplied either in a gaseous or a fluid form, 

 and hence the necessity for the various changes which are constantly 

 going on in the soil, and which are aided by the efforts of man. 

 Plants are capable of deriving all their nourishment from the mineral 

 kingdom. The first created plants in all probability did so, but in the 

 present day the decaying remains of other plants and of animals are 

 also concerned hi the support of vegetation. 



Organic Constituents and their Sources. 



212. Carbon (C) is the most abundant element hi plants. It forms 

 from 40 to 50 per cent, of all the plants usually cultivated for food. When 

 plants are charred the carbon is left, and as it enters into all the tissues, 

 although the weight of the plants is diminished by the process, their form 

 still remains. When converted into coal (a form of carbon), plants are 

 frequently so much altered by pressure as to lose their structure, but 

 occasionally it can be detected under the microscope. Carbon is insoluble, 

 and therefore cannot be absorbed in its uncombined state. When 

 united to oxygen, however, hi the form of carbonic acid, it is readily 

 taken up either hi its gaseous state by the leaves, or hi combination with 

 water by the roots. The soil contains carbon (humus), and in some soils, 

 as those of a peaty nature, it exists in very large quantity. The carbon 

 in the soil is converted into carbonic acid in order to be made avail- 

 able for the purpose of plant-growth. Carbon has the power of absorb- 

 ing gases, and in this way, by enabling certain combinations to go on, it 

 assists in the nourishment of plants. In the atmosphere, carbonic acid 

 is always present, averaging about ^^ part, arising from the respir- 

 ation of man and animals, combustion, and other processes. 



