This section is from the book "British Wild Flowers - In Their Natural Haunts Vol2-4", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
A cart-road is very similar to an ordinary roadside, along which, as has been shown (Section VI), a number of plants are dispersed by artificial agency. The highway, however, is regularly made up with macadam, whereas the cart-road is more or less left to itself, and the ruts and middle way alone are regularly used, whilst the intervening spaces are grass-grown, or loose or broken. Upon such spots a number of plants grow which are foreign to the pasture through which such cart-ways are made to reach the highway; also along roads that are primarily used for agricultural purposes.
Naturally the character of the weeds so dispersed depends largely upon the character of the arable or pasture. It is an interesting study to trace the distribution of such weeds from their probable source, and the process by which this has been accomplished. The White Campion is one of the most prevalent plants distributed by this means. Viper's Bugloss is a handsome plant which is frequent upon chalky soils, but may be found elsewhere distributed by farming operations. The Corncockle, now rare in cornfields, is to be found by the side of a cart-track, or more frequently in some districts in or near a fowl-run, dispersed in fowl corn. On sandy soils Knotted Hedge Parsley is often to be found on the side of cart ruts, its usual habitat being a hedge bank.
Melilot is found on towing-paths and in other waste places. Mayweed is a common straggler along the cart-road. Wormwood is conspicuous in hedges along the borders of arable fields or the roads that lead from them. The Burdock, Chicory, Yellow Toadflax, and Hemp Nettle are others that should be mentioned here.
One of the most potent factors in the distribution of weeds of cultivation and aliens is the railway or the canal. The railway embankment, especially in low-lying areas, forms a direct barrier to the dispersal of seeds blown by the wind across country. The embankment, which is often lofty, thus tends to accumulate or "make a corner in" the seeds so dispersed. And although a great number of such seeds doubtless do not come to maturity, yet a large proportion evidently do survive; and once they have gained a foothold manage to persist in a remarkably successful manner.
The same remarks apply to a canal, which, though not usually cut through embankments affords the same means of dispersal, though the plants dispersed are not usually of the same species.
The mode of dispersal along railways and canals is difficult to determine. Many plants, apart from the part played by the track as a barrier, are dispersed by falling out, or blowing out, of seeds from goods wagons. In the upkeep of the line, or the canal, horse traffic is responsible for the dispersion of fodder plants. The goods yard and the coal wharf are centres of distribution of such plants, and so are colliery sidings. The gardens maintained by railway employees along the line are also important factors in the spreading of plants along the line. Plants commonly found on railway banks are the Toadflaxes (including hybrids), Melilot. Mountain Crane's Bill, Euphorbia Cyparissias, Anthyllis Vulneraria, Lamb's Lettuce, Brassica Napus.