IV PLANT LIFE 39 



all the four organic elements — and known as nitrogenous. 

 In the former class are included cellulose or woody material, 

 starch, sugar, gums, &c. : and in the latter class are 

 included protoplasm a?id chlorophyll. Protoplasm is that importance 

 part of the plant in which the principal vital functions are plasm. 

 centred, and chlorophyll is the colouring matter of the 

 leaves, and it is the agent specially concerned in decom- 

 posmg carbonic acid so that the carbon is retained by the 

 plant, and the oxygen is returned to the atmosphere. The 

 inorganic portions of plants are silica, chlorine, potash, soda, 

 magnesia, lime, oxide oj i7'on, phosphoric acid, and sulphuric 

 acid J sometimes, manganese and other mineral substances 

 may be found in minute proportions. These organic 

 elements do not occur by themselves or in a free condition, 

 but they unite with each other to form compounds, as for 

 instance in the superphosphate of lime which is composed 

 of phosphorus, calcium, hydrogen and oxygen. A knowledge The im- 



/• -I 1 /-I • r t portance 



of the composition of the ashes of plants is of the greatest ofchemkai 

 use to planters, for they are then able to determine whether pj!fiJ5J^^ °^ 

 a particular plant can be grown with success on certain 

 portions of their lands. Thus, if the land be deficient in 

 lime, and the planter wishes to grow plants that take up 

 much lime, he knows that the plants will not grow properly 

 unless he gives lime to the soil in some way or other. The 

 inorganic parts of the plants, as shown by the quantity of 

 ash, are very small, but they are as necessary to the well- 

 being of the plant as is the water which is contained in the 

 tissues in such abundance. A soil in which all but one of Soils should 



contam all 



the necessary inorganic elements are found will not grow the inorganic 

 the plant, for the absence of the element occurring in the found"in 

 ashes in the smallest quantity renders the soil less able to ^^^ plants. 

 produce luxuriant vegetation of the sort desired. This 

 explains the wonderful help that agricultural chemistry 

 renders to the farmer or planter. He first finds out what is Value of 



1 • • r 1 1 1 • 1 111 agricultural 



the composition of the plant he wishes to grow, and then he chemistry, 

 has his soil analysed so as to see whether it contains all the 



