Evolution of Soils. v7 
stance over the rock, sending its fibers into the 
crevices and filling the chinks, as they enlarge, with 
the decay of its own structure; and finally the 
rock is fit for the moss or fern or creeping vine, each 
newcomer leaving its impress by which some later 
newcomer may profit. Finally the rock is disinte- 
grated and comminuted, and is ready to be still 
further claborated by corn and ragweed. Nature 
intends to leave no vacant or bare surfaces. She 
providently covers the railway embankment with 
quack-grass or willows, and she seatters daisies in 
the old meadows where the land has grown sick 
and tired of grass. If one pulls up a_ weed, he 
must quickly fill the hole with some other plant, or 
nature will tuck another weed into it. Man is yet 
too ignorant or too negligent to eare for the land, 
and nature must still stand at his back and sup- 
plement the work which he so shabbily performs. 
She knows no plants as weeds. They are all 
equally useful to her. It is only when we come to 
covet some plant that all those which attempt to 
crowd it out become weeds to us. If, therefore, we 
are competent to make a choice of plants in the first 
place, we should also be able to maintain the 
choice against intruders. It is only a question of 
which plants we desire to cultivate. 
We must keep the land at work, for it grows 
richer and better for the exercise. A good crop on 
the land, aided by good tillage, will keep down all 
weeds. The weeds do not “run out” the sod, but 
the sod has grown weak through some fault of 
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