42 THE FOOD OF PLANTS CHAP. 



to fill the test-tube with this gas, and hold the test- 

 tube in the flame of a lamp. 



The cress seed begins to smoke. Continue 

 heating it till the smoke ceases to come off, then let 

 it cool, and empty the contents on to a watch-glass. 



The seeds have been reduced to charcoal. Weigh. 



Let us now heat the dried cress in the platinum 

 dish for a few seconds over a spirit lamp, so as to 

 reduce it to charcoal, and weigh. 



The charcoal obtained from the seed weighs a good 

 deal less than that obtained from the dried plants. 



We have found by this experiment, not 

 only that the dried plants weigh more than 

 the seeds, but also that the dried plants con- 

 sist partly of charcoal, and that only some of 

 this charcoal has come from the seeds. 



Let us search on every side, and try and find 

 from what source this charcoal can have come. 



We have seen that plants are largely composed of 

 charcoal. Are animals also largely composed of this 

 substance 1 



Let us find out by repeating on a piece of meat 

 the experiment we made with the dried cress. 



Smoke is given off, and a mass of charcoal is left 

 behind. 



Animals as well as vegetables then can be trans- 

 formed in part into charcoal. 



We have still, however, to find out where the plant 

 obtains the charcoal from, and with a view to helping 

 you towards that discovery, I would ask you to 



