THE FOOD OF PLANTS. 



129 



with soda-lime. A similar observation has been made by Hermann who 

 found that rotting wood fixes nitrogen, producing a nitrogenous body 

 which he terms "nitrolin." Mulder was of opinion, and in this he is 

 supported by various recent observers, that nitrogen is fixed by a soil 

 rich in humus, a view which is supported by Berthelot's experiments 

 mentioned above. The subject cannot, however, be regarded as fully 

 investigated at present. 



A few words may be added here with reference to the loss of combined 

 nitrogen in nature. Living organisms probably effect no change in the 

 total quantity of combined nitrogen; their nitrogenous waste-products 

 are all compounds of nitrogen. It appears that a certain loss of combined 

 nitrogen attends the putrefaction of nitrogenous organic substances and 

 especially their combustion, free nitrogen being evolved. 



Another point of interest may be briefly referred to, namely this, that 

 there is going on in the soil a process by which the ammonia supplied to 

 the soil as manure or which is formed there by the decomposition of 

 nitrogenous organic substances is converted into nitrous and this into nitric 

 acid. These processes are termed "nitrification," and are effected by 

 means of organised ferments of the nature of Micrococci (Warrington, 

 Schlosing and Miintz). 



With regard to the elements constituting the ash, it may 

 be repeated here (see p. 61) that their absorption by the 

 plant depends essentially upon the activity of its metabolism. 

 This is well shewn in the following table of analyses by 

 Arendt. 



He analysed 1000 Oat-plants at various stages of their growth : the 

 figures give the quantity in grammes of each ash-constituent present. 



Total Ash 



37'i2 72*20 101-36 124*54 128-04 



It must be remembered, however, that although the absolute amount 

 of ash increases with the age of the plant, the proportion of ash to the dry 

 solid diminishes. 



V. 



