THE MATERIAL OF PLANTS 11 



will have first the weight of the fresh material, 

 about half a pound. Wheu the fresh plant is 

 dried, it needs no demonstration to show that water 

 is driven off, so that the next weight represents 

 the material in the plant after the water is taken 

 away. This dried material is composed of two dif- 

 ferent kinds of substances. When it is burned, 

 one kind, constituting the charcoal, is consumed, 

 leaving only the ash or mineral substances behind. 

 If these weighings are carefully made, it will be 

 found that the water makes more than three-fourths 

 of a growing plant, the charcoal generally less 

 than one-fourth, and the ash only one-fortieth or 

 one-fiftieth of the total weight. The ashes that col- 

 lect in a stove are exactly similar to those obtained 

 in this experiment, of course ; and it is well known 

 that the weight of the ash from a heavy armful of 

 wood is very small. This experiment may also be 

 carried out with a potato, carrot, or turnip. 



The relative amounts of the different groups of 

 substances vary with the species of plants exam- 

 ined and the age of the specimens. The greatest 

 proportion of water is to be found in young shoots, 

 the greatest proportion of charcoal in old woody 

 stems, and the greatest proportion of ash in leaves. 



