n8 Master Minds of Moder?t Science 



yet they multiply so fast that under perfect conditions 

 one of them might in a day become the ancestor 

 of 280,000,000,000,000. 



Bacteria are responsible alike for the flavours of butter 

 and tobacco and for the smell of a dead mouse. Their 

 most important job is the breaking down of manure and 

 other organic substances into food for plants. One race 

 of bacteria turns the dead plants into humus, another into 

 nitrate and into the other substances on which plants live. 

 Even such tough stuff as wheat straw is broken down by 

 them and converted into plant food. 



One of the things that scientists have found out is 

 exactly what plants do live upon. They have discovered 

 precisely how a plant feeds and under what conditions of 

 food, moisture, and warmth it most quickly reaches its 

 full growth. The first step in this direction was the 

 analysis of plants. 



Take a living plant and reduce it to its elements ; it 

 will be found that water is its most important constituent ; 

 next comes carbon. Of the dry matter of the plant fully 

 half is carbon; oxygen and hydrogen compose most of 

 the remainder, with a certain number of other elements, 

 one of them being nitrogen. The amount of nitrogen is 

 small, being only about one-fiftieth of the dry matter, yet 

 nitrogen is so important that no plant can exist with- 

 out it. The remaining ash is formed of a number of 

 other elements, phosphorus, silicon, chlorine, and the 

 metals potassium, sodium, calcium, magnesium, iron, and 

 manganese. 



Interesting, no doubt, you will say, yet crops were 

 grown long before people had any knowledge of these 

 facts. Our ancestors also used manures to make their 

 crops grow. That is true. Such things as dung and leaf 

 mould, chalk and marl, have been used from time im- 

 memorial, but they were used blindly. 



So far as we know, the first artificial manure to be used 



