90 LIFE OF A TREE. 
may generally impress us, there is not a leaf 
among the countless millions of the forest, nor 
a blade among the green army of the meadow- 
grass, which is not of importance to mankind 
and to the brute creation. 
Nothing grows in vain. The least flower has 
a part of the great work of purification of the 
air, that falls to it; for although it might not 
be missed out of the innumerable ranks which 
adorn the garden or the wayside, we must not 
forget that the whole universe is made up of a 
combination of little things, and though the im- 
portance of a tiny plant may be little in itself, 
it forms one of a number, which however vast 
is, after all, only made up of individuals, each 
having a share in the task to be done. We 
might go even lower in the scale, and say, each 
little cell of the green duckweed floating in our 
quiet pools has its share of work; for it is an 
interesting discovery, that even these little masses 
of vegetation exercise a purifying influence upon 
the boundless air. 
Yet we must not forget to mention, that a 
most remarkable class of exceptions to this rule 
is known to Botanists. These are the curious 
