74 MINUTE MARVELS OF NATURE 



developed in some of the plants which we have 

 been considering. 



Having now glanced at the structure of various 

 types of leaves, before considering the purposes 

 of their various cellular divisions, let us roughly 

 analyse a green leaf and see of what elements 

 it is mainly composed. We take a few fresh green 

 leaves and carefully weigh them on a chemical 

 balance so as to be exact. Having taken their 

 precise weight, we place them in an arrangement 

 over a lamp where they may be heated to a tem- 

 perature equal to that of boiling water, and leave 

 them there for several hours ; after which we re- 

 move them and weigh again. Of course they have 

 dried up, having parted with their moisture, and 

 on weighing we find that they have lost about 

 four-fifths of their original weight. So it is plain 

 that four-fifths of their original weight was water, 

 which has been driven off as vapour by the 

 heat. 



The leaves may now again be heated in a suit- 

 able vessel until they burst into flame. After 

 burning, there remain only charred bits of carbon 

 or charcoal, which may be allowed to burn on 

 until nothing is left but a grey ash. This ash we 

 can destroy no further by burning, as it is the 

 indestructible mineral residuum of the leaf. After 

 allowing it to cool, we weigh this ash and find a 



