CHAPTER XVII 

 MINERAL NUTRIENTS AND NITROGEN 

 Ash Content of Plants.— We have already learned that water 

 constitutes about four-fifths of the ordinary herbaceous plant. If 

 the plant is dried thoroughly and the remaining one-fifth of 

 solid matter is burned in an open fire, we have a comparatively 

 small am.ount of ash, which is usually about 1 to 3 per cent, of 

 the original dry weight, although in some cases it is greater. 

 The other 17 or 19 per cent, is orgajiici material which has been 

 volatilized. The ash contains the minerals of the plant, which 

 have been obtained from the soil. The percentages of solids and 

 ash for a few plants are given in the following table : 



Ash per cent 



Product Total Solids of total product 



Green corn fodder 20.67 1.16 



Ripe corn fodder 89.44 1.53 



Ripe wheat (grain only) 89.48 1.87 



Green timothy hay 38.42 2.10 



Green clover hay 29.21 2.10 



Red beets 11.53 1.04 



Cabbage 9.48 1.40 



Lettuce 4.13 1.49 



Cucumber 4.01 .46 



The ash contains small amounts of practically all the min- 

 erals found in the soil in which the plant was grown. If the 

 minerals of the soil are soluble, they will be taken into the plant, 

 unless prevented by the plasmatic membranes of the root-hairs, 

 which have a certain selective power (see page 163). The 

 minesral elements most commonly found in plants are: phos- 

 phorus, potassium, calcium, magnesium, sulfur, iron, sodium, 



chlorine, silicon, manganese and aluminum. 



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