CH. IX. "i DEATH AND DECOMPOSITION. 329 



serve green peas. These are put into diy glass bot- 

 tles, and the bottles placed in water, then gradually 

 made to boil. The chief part of the air is thus driven 

 from the bottles and they are corked do^vn tightly, 

 and the cork rosined over whilst thus heated. What 

 little oxygen remains in the bottles is absorbed by 

 the peas, and these remain green and unaltered for 

 months, requiring only the addition of a little soda 

 to the water in which they are boiled, to be as 

 tender nearly as when first gathered. 



When a temperature of 45^, moistui'e, and atmo- 

 spheric air occur to dead vegetable matters, they ab- 

 sorb large quantities of oxygen, evolving also an equal 

 volume of carbonic acid. If composed of carbon, 

 hydrogen, and oxygen only, the fumes they emit are 

 not offensive ; but if, as in the case of onions and 

 the cabbage tribe, they contain a considerable por- 

 tion of azote, the smells emitted are disgusting. 



As in all other instances where vegetable sub- 

 stances absorb oxygen gas in large quantities, much 

 heat is evolved by them when putrefying ; and advan- 

 tage is taken of this by employing leaves, stable 

 litter, and tan, as well known sources of heat in the 

 gardener's forcing department. 



^^^len the putrefactive process of plants is com- 

 pleted, there remains a soft black mass, known as 

 vegetable mould, or humus. One hundred parts of 

 the humus of wheat straw have of extractive or 



