HOW NATURE STUDY SHOULD BE TAUGHT 1 25 



earth, since it absorbs the inorganic matters which 

 it needs for its food, as they percolate in solution 

 through the soil. The student of inorganic chem- 

 istry knows what these are, and that they may be 

 supplied to the plant under investigation, without 

 the intervention of the soil. All that is needed is 

 some material, be it sawdust, pebbles, shot, beads, 

 or any other substance through which the roots 

 may pass, to seek the food artificially applied to 

 this artificial soil. As honey may be purchased 

 in the market, and supplied to the bees by spread- 

 ing it on almost any convenient material, so that 

 they may have easy access to it, so this chemically 

 isolated nutriment may be manufactured in a form 

 convenient for solution in the water which is poured 

 over the substance that upholds the plant and 

 gives the rootlets easy access to their food supply. 

 Several botanical chemists have provided such 

 food. Perhaps the best is that made according to 

 the following formula by Professor Sachs, and 

 pressed into tablets for the sake of convenience. 

 Each of these tablets is composed of the follow- 

 ing : 



Metric weight (nearly) 

 Common table salt (Sodium chloride, NaCl), 



2 grains. .162 grams. 

 Plaster of Paris — Gypsum (Calcium sulphate, CaSO 4), 



2 grains. .162 grams. 



