100 AGRONOMY 



Chlorine, silicon, and others. Small amounts of chlorine, 

 silicon, sodium, manganese, aluminum, and other minerals are 

 usually found in the ash of plants. They are present in most 

 soils and, being dissolved in the soil water, flow into the plant 

 with it. Silicon is often abundant in the older, denser parts 

 of plants, and the flinty exterior of scouring rushes and grass 

 stems is due to it. The " shells " of diatoms and the stems of 

 certain scouring rushes contain so much silicon or silica that 

 the organic parts may be burned or dissolved out, leaving a 

 perfect skeleton of the mineral. Silica, however, does not 

 appear to be essential to the life of the plant. It was once 

 thought that it was necessary to give strength to the stems of 

 grasses and other plants, but this is shown to be a mistake 

 by the fact that silica is often many times more abundant 

 in the leaves of plants than in their stems. Some regard 

 chlorine as essential, since it is usually present in the plant. 



PRACTICAL EXERCISES 



1. Take two geranium leaves and place one in fresh water and the 

 other in a 10 per cent salt solution for half an hour. Explain the dif- 

 ference in the two. 



2. AVeigh a good-sized potato and thoroughly dry it by heating in 

 an oven. Weigh again. What per cent of moisture did it contain ? Place 

 in a crucible and heat to redness to drive off the organic matter. What 

 per cent is ash ? 



3. Thoroughly water a pot of young oat seedlings and turn a bell 

 jar over them. Account for the drops of water that soon appear on the 

 tips of the leaves. The same experiment may be performed with nas- 

 turtium or fuchsia plants if oats are not at hand. 



4. Clover hay may yield three tons to the acre. How many inches 

 of rainfall would be needed to supply the necessary moisture if none 

 were wasted and the plants used 250 pounds of water in producing 

 each pound of dry matter? 



References 



Hopkins, " Soil Fertility and Permanent Agriculture." 

 Snyder, " Chemistry of Animals and Plants." 



