While some relations among organisms are readily appar-ent, most are not easily observed.
The distribution of plants has long bemused botanists. Certain plants live in widely separated places. The same plant may live in the upper reaches of North America and the tip of South America, but nowhere in-between.
Migratory birds may trap and carry in their feathers small plant parts with them on their journeys. Mosses, which are especially rugged, are common passengers. After a bird cleans itself from the trek, deposited stowa-ways establish a new population in a new land.