Read it through once

Weeds are an extremely interesting group. A proverb about the hardiness and multiplication of weeds can be discovered in almost every language. "Ill weeds grow apace," _Unkraut verbessert nicht_, and so on. They are very common. In fact weeds, wayside, and freshwater plants, have by far the widest distribution of all. There are twenty-five species which can be found over at least half the entire land surface of the earth, and more than a hundred occupy a third of it.[122]