6 4 
THE GARDEN OF THE WORLD 
Why is clover 
good for the 
grass? 
tips of its leaves are little bladders or bags. Each 
bladder has a remarkable little trap door at the 
end of it. This door opens at a touch from the 
outside, but will not open at all from within. 
Tiny water creatures brush against the trap door 
and instantly find themselves inside the bladder. 
There is no-escape possible, so they die and then 
decay to be used as plant food. The bladder- 
wort catches only tiny creatures. Some of them 
are so small that a strong magnifying glass is 
needed to see them at all. 
Long before anyone knew the reason, gar¬ 
deners and farmers knew that clover was good 
for the soil. A farmer found that if he had a 
field of clover one year and planted corn the 
next year, his corn would be better in that field 
than in any other. The reason is interesting. 
Next to carbon dioxide and water, the most 
important element that plants need is nitrogen. 
Nitrogen is very plentiful in the air. It is about 
us all the time, but unfortunately plants cannot 
use it in that form. They can only get it when 
it is in the soil combined with other elements. 
