2 WHAT THE PLANT IS MADE OF [chap. 



that the contents have lost a good deal of water, 

 amounting to 80 to 90 per cent, of the original weight 

 of the green leaves ; the roots lose nearly as much, 

 but the seeds only 10 to 15 per cent. 



Water is an invariable, and indeed the chief 

 constituent of the living plant. 



Take now the dry plant tissues still in their basins, 

 and heat them more strongly over the Bunsen or 

 Argand flame, covering the greater part of the basins 

 with a sheet of metal. Thick gases possessing a 

 pungent smell will be given off, and these after a time 

 will take fire if allowed to come in contact with the 

 lamp ; after a time extinguish the flame by completely 

 covering the basin, and cease heating until the contents 

 are cool enough for examination. It will now be seen 

 that the whole interior of the basin is covered with 

 black soot, and that the plant material is charred or 

 carbonised ; there is abundant evidence that the black 

 element. Carbon, has been set free from the original 

 plant tissues. Now resume the heating, but without 

 any covering, push it as rapidly as possible, and let the 

 contents of the basins burn away until little or nothing 

 of the black carbon is left, though to get rid of the last 

 traces it may be necessary to put the basins in a 

 muffle furnace and raise the contents to a bright red 

 heat. At the end, when everything possible has been 

 burnt away, there will still be found a little grey or 

 white ash, which on weighing will amount to from 2 to 5 

 per cent, of the dry matter that was left after the water 

 had been driven off. In the plant ash only a few 

 elements are to be found, but these are the same what- 

 ever the plant or wherever it has been grown, with a few 

 exceptions that are small and unimportant. By tests 

 which need not here be detailed, we can always demon- 

 strate in the plant's ash the presence of the elements 



