NUTRITIVE FUNCTIONS OF SALTS 113 



Total Ash Content.— If the proportions of the individual ash 

 constituents change with age and the other above-mentioned con- 

 ditions, no less can be said for the total ash content, the specific 

 variation of which is shown by the following table : 



Total per cent of dry weight in ash 



Apples 0.4 Hops (leaves) 13.6 Scotch pine 5.9 



Beets 6.0 Onions 5.2 Tobacco (leaves) 11.9 



Carrots 5.4 Potatoes 4.0 Tobacco (stems) 7.7 



Chicory 6.2 Rice 1.2 Wheat (seeds) 2.0 



Fruits, especially fleshy fruits with a high water content, have the 

 lowest percentage of ash, and leaves have the highest, probably 

 owing to the fact that the water leaves the ash behind as it evap- 

 orates from them in transpiration. It is common knowledge that 

 burning leaves give more ash than other plant parts. 



The nature of the soil and the environment will also cause a 

 variation in the total ash content. With a high salt content in 

 the soil the total ash will be higher than when the salt content of 

 the environment is at a minimum, although it should be added 

 that this statement is true only for total ash and not for any indi- 

 vidual salt. Sugar beet ash content has been found to vary from 

 3.5 to 14.5% of the dry weight, depending upon the varying en- 

 vironmental conditions of light, temperature, soil, and the available 



water. 



The total ash also varies with the age of the plant. Arendt 

 determined that for oats the total percentage of ash varied from 

 8.57% when three leaves had unfolded to 5.40% at maturity. 

 The following figures (from Molliard) have been found for wheat: 



Per cent 

 Ag e ash content 



Very young stem 3.6 



30 days old 7.8 



15 days before blooming " 8.5 



In bloom 6.2 



Matured 5.0 



These figures must not be interpreted to mean that the total ash 

 is diminished, but must be interpreted in terms of a decreasing 

 water content as well as an increased dry weight. 



Nutrient Solutions.— For experimental purposes, nutrient solu- 

 tions of distilled water and the essential elements are prepared. 

 The plants may be grown with their roots in the solution, or the 

 solution may be poured over clean sterile quartz sand and the 



