M 
THE GARDEN OF THE WORLD 
algae are very important to us. They are not 
good for food, and they are not even dangerous 
as some of the simple plants, like bacteria, are. 
People often have an idea that pond scum is 
poisonous. It really is harmless, but the water 
in these ponds often contains poisonous bacteria 
so it is not safe for drinking. 
If the algae are not important in themselves, 
however, they are very important in the history 
of plants. Probably the very first plants in the 
world were one-celled just like the green scum 
floating on ponds. Gradually, through millions 
of years, they changed and finally became the 
complicated plants with stems, leaves and roots 
which we have now. We are sure that the very 
first plants grew in the water because simple 
plants can grow much better there. They do 
not have to provide against drying out as the 
land plants do. Every living cell must be full 
of water. This is always true whether the cell 
is growing alone or as one of many in a large 
and complicated plant. It is true of animal 
cells also. Plants which do not live in water 
