The reason such trees as the pines, poplars, and willows come first is that the seeds are so light they are easily carried by the winds and so reach new soil ahead of other trees with winged seeds like the beeches and the maples; for, although these seeds also travel on the wind, they are much larger than the winged seeds of the pine and they travel much more slowly and for shorter distances. Moreover, at the end of their first journey, having once fallen to the ground, they are apt to stay. Then there is no further advance, so far as these particular seeds are concerned, until trees have sprung from them and they, in turn, bear seeds. In the case of very light seeds, like those of the pines, the wind not only carries them far beyond the comparatively slow and heavy march of the beech and the maple, but if they fall on rock with little or no soil the next wind picks them up and carries them farther, so that they may strike some other spot where there is soil and perhaps a little network of grass and weeds to secure them until they can take root and so hold their own. It is not only a great advantage to the pine seeds to be so small, so far as getting ahead of other trees is concerned, but it is an advantage in another way. Because they are so small they require comparatively little soil to start with, are more easily covered up, and so they soon begin to sprout. The very winds that carry them up among the mountain rocks are quite likely to cover them with enough dust to start on, and I myself have helped raise many a giant of the mountain forests in this way. It is really wonderful how little soil a pine-tree can get along with; if, say, its fortunes are cast on some mass of mountain rock. Somehow it manages to get a living among the cracks and at the same time to hold its own in the bitter struggle with the winds. "The pine trees," says Muir, "march up the sun-warmed moraines in long hopeful files, taking the ground and establishing themselves as soon as it is ready for them." [Illustration: _From the painting by Rousseau in the Metropolitan Museum of Art._ THE EDGE OF THE WOODS Last of all come tramping along the sturdy old oaks.] Last of all come tramping along the sturdy old oaks and the nut-bearing trees. Their seeds are so heavy they get little help from the winds, and then only in the most violent storms. They must advance very slowly indeed, with occasional help from absent-minded squirrels who carry away and bury nuts and acorns and then forget where they put them. [Illustration: HOW SQUIRRELS HELP OAKS TO MARCH Sometimes they bury acorns and forget just where. When frightened they often drop them and run away.] ROUGH CITIZENS AMONG THE PIONEERS