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 cornfield characters are in many respects similar to those of grass fields, meadow, or pasture. Within the term cornfields are included all types of arable or cultivated land which are subjected to the plough, a factor which is of the greatest importance. For this mechanical instrument alone causes all the difference between the close grass of the meadow surface and the open broken ground of the cornfield.
The first characteristic common to ordinary fields and cornfields and allied cultivated tracts is their accessibility. At least the margins of such fields usually grassed over may be examined.
They were once like meadows occupied by woodlands, and in many cases common land. Their expansiveness is similar (though they are less continuous) to that of meadows. The cornfield plants are sun plants, though the ground flora, as in meadows, is obscured by the higher zones. This is one of their most marked characteristics. As in the case of meadows, some are lowland, some are upland, but few range above an altitude of 1000 ft., whereas meadows occur at higher levels.