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.
The soil conditions of the cornfield exhibit a striking similarity to those of the waste place and kindred habitats. It might be in some ways better to combine the two. But there is in the first place a greater similarity between the character of the meadow and the cornfield, the origin of which is the same; and in the second place there is a marked difference between the character of the cornfield and all cultivated land, and that of the waste place. For in the former certain definite operations are continually going on which are responsible very largely for the associated cornfield wild plants, whilst the very nature of the waste places, and the absence of any such operations, renders such habitats entirely lacking in the chief characteristics that distinguish cultivated land from all other types.
None the less the essential connection between many descriptions of waste place associated with farming causes the flora of the two to be essentially similar. For there is, in the first place, a continual carting of materials from the cornfield to stackyards and similar storage areas, when seeds are being continually dropped or dispersed, so that their range is extended. In the second place, waste ground is usually broken and open, and thus suited to the colonization of plants derived from cornfields. In the third place, the origin of the waste-ground plants, such as aliens and casuals, is essentially the same. They have been brought from elsewhere by the same agencies.