TBJS WOMK OF ROOTS 137 



matters absorbed by the plant ? We may easily answer 

 this question by burning the plant, since whatever 

 remains after thorough burning represents mineral 

 matters which have been absorbed by the plant. "We 

 first dry the plant thoroughly in the sun or in an oven ; 

 we then break it into small pieces, place them on a 

 small iron shovel and heat it red-hot. Continue the 

 heating until the ash becomes white, or nearly so, on 

 cooling. 



If we weigh the plant before and after drying, and 

 also the ash left after burning, we shall know approxi- 

 mately how much water, how much cellulose (see page 

 66) or woody fiber (the combustible part), and how 

 much mineral matter it con- 

 tains. 



Is the absorbed mineral 

 matter of use to the plant ? 

 In order to deprive the plant 

 of its supply of mineral mat- 

 ter, we must furnish it with 

 distilled water instead of or- 



T . , -TTT 1 95. A still for making distilled water; 



dmary water. We may ob- it consists of two pans and a eake- 



tain distilled water by means *" <'»" °* graniteware or tinware). 



of the apparatus shown in Fig. 95. It consists of 

 two pans and a cake-tin, the central cone of which 

 has been shortened to the proper length by making 

 vertical cuts with a pair of stout shears and then bend- 

 ing back the flaps as shown in the figure. Water is 



