This section is from the book "Commercial Gardening Vol4", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
The principal crops grown are Radishes, Lettuces (Cos and Cabbage varieties), Endive, Carrots, Cauliflowers, Turnips, Spinach, Celery, and Canteloupe Melons. These may be regarded as the standard crops, but Corn Salad, Cucumbers, Tomatoes, Aubergines, Cabbages, Sorrel, Leeks, Onions, etc, are sometimes grown as catch crops.
It may be well to say a little about each of the principal crops in alphabetical order.