Read it through once

Yet these tall Thistles and Ragweeds are only the first stage of a very interesting invasion. Look around the field corners, on railway-banks, or in old quarries, where man has left things alone. You will see these same tall herbs (the Ragweed, etc.), but you are sure to find a place where they are being suppressed by Rasps, Briers, and Brambles. These are taller, stronger, and more vigorous than the herbs, and they also last longer, for their leaves are still at work in November. This is the second stage of the invasion. But if the place has been long neglected, Hawthorns and Rowans, Birch and Ash will be found growing up. These last show what is happening.