The grouping of vegetables gives the student a better understanding of the character, requirements and uses of the various crops. The arrangement based solely upon botanical relationship is the most exact system, but in many cases is of little advantage in helping to determine the best cultural conditions for each crop. The uses of the plants also constitute an important basis for classification. All vegetables may be placed in two general groups in respect to their hardiness, viz., (1) "tender" plants, or those which are injured or killed by frost, and which require high temperatures for successful growth, as tomato, pepper, eggplant, bean, melons, squash, cucumber, sweet corn and sweet potato; (2) "hardy" plants, or those which are not injured by frost, many of them in fact bearing severe freezing and thriving at temperatures too low for "tender" plants. The "hardy" crops include pea, cabbage, kale, spinach, asparagus, rhubarb, celery, lettuce, cress, radish and many other plants. The line, however, between "tender" and "hardy" plants is largely arbitrary. Celery, for example, is properly classed with hardy plants, while comparatively light frost or low temperatures may check the growth of young plants and cause them to produce seed shoots. The onion is also regarded as a hardy plant, while seedlings of certain varieties are injured by light frosts.

The best system of classification has been devised by Prof. L. H. Bailey ("The Principles of Vegetable Gardening," pp. 240-242), and is followed in this chapter. It is based primarily upon methods of culture, although other factors are considered. The system provides for two general classes; namely, annual vegetables and perennial vegetables. These classes are then divided in subclasses according to the uses of the crops, and each subclass is composed of groups, determined mainly by their cultural requirements. The scheme of classification proposed by Professor Bailey is as follows:

Class I. Annual Vegetables. Subclass I. Crops Grown For Subterranean Parts

Group 1. Root Crops

Beet (Beta vulgaris). Carrot (Daucus carota). Celeriac (Apium graveolens). Chicory (Cichorium intybus). Horse-radish* (Cochlearia armoracia). Parsnip (Pastinaca sativa). Radish (Raphanus sativus). Salsify (Tragopogon porrifolius). Turnip and Rutabaga (Brassica).

Group 2. Tuber Crops

Sweet potato (Ipomoea batatas).

Group 3. Bulb Crops

Cive or Chive (Allium schoenoprasum). Garlic (A. sativum). Leek (A. porrum). Onion (A. cepa, A. fistulosum). Shallot (A. ascalonicum).

Subclass II. Crops Grown For Foliage Parts

Group 4. Cole Crops

Broccoli (Brassica oleracea). Brussels sprouts (B. oleracea). Cabbage (B. oleracea). Collard (B. oleracea). Cauliflower (B. oleracea).

Kale (B. oleracea).

Kohl-rabi (B. oleracea).

* Horse-radish and dandelion are perennials but usually occupy the ground only one year.

Group 5. Pot Herbs (Used For "Greens")

Beet (Beta vulgaris).

Chard (B. vulgaris).

Dandelion (Taraxacum officinale).

Mustard (Brassica species,).

Sea kale (Crambe maritima). Spinach (spinacea oleracea).

Group 6. Salad Crops

Celery (Apium graveolens).

Corn salad (Valerianella olitoria).

Ciess (Lepidium sativum, Barbarea vulgaris, Nasturtium officinale). Endive (Cichorium endiva). Lettuce (Lactuca sativa). Parsley (Carum petroselinum).

Subclass III. Crops Grown For Fruit Or Seed Parts

Group 7. Pulse Crops

Bean (Phaseolus, Dolochos, Vicia).

Pea (Pisum sativum).

Group 8. Solanaceous Crops

Eggplant (Solatium melongena).

Pepper (Capsicum annuum). Tomato (Lycopersicum esculentum).

Tomato, husk or strawberry (Physalis).

Group 9. Cucurbitous Or Vine Crops

Cucumber (Cucumis sativus).

Gherkin (C. auguria).

Muskmelon (C. melo).

Pumpkin (Cucurbita).

Squash (Cucurbita).

Watermelon (Citrullus vulgaris).

Group 10. Corn, Okra, Martynia

Martynia (Martynia proboscidia).

Okra (Hibiscus esculentus).

Sweet corn (Zea mays).

Group 11. Condimental And Sweet Herbs

Dill, mint, sage, savory, tansy, thyme and many others.

Group 12. Mushroom

Not discussed in this book. It is more generally regarded as a forcing crop.

Class II. Perennial Vegetables

Artichoke, globe (Cynara scolymus). Artichoke, Jerusalem (Helianthus tuberosus). Asparagus (Asparagus officinalis). Rhubarb (Rheum rhaponticum).

Sea kale (Crambe maritima).

261. Requirements Of The Various Groups

Root crops (Group 1) thrive at comparatively low temperatures. They usually prefer sandy loams, and deep soils are also important for long-rooted crops. Sandy types of soil favor symmetrical development of roots and decrease the percentage of the small, fibrous roots objectionable in this class of vegetables.

Tuber Crops (Group 2)

The sweet potato requires a long season and high temperatures. Sandy soils are preferred.

Bulb Crops

Bulb Crops (Group 3) are hardy and may be grown successfully in many soil types, although sandy loams are best. They do not require high temperatures, but the soil must be well provided with humus and available plant food.

Cole Crops

Cole Crops (Group 4) are hardy and require a cool season, a fertile soil and an abundant supply of moisture.

Potherb Crops

The requirements of the "greens" (Group 5) are variable. (See Chapter XXI).

Salad Crops

Salad Crops (Group 6) are hardy. They require liberal feeding and an abundance of moisture.

Pulse Crops

(Group 7) Soil and weather requirements vary with each crop.

Solanaceous Crops

Solanaceous Crops (Group 8) are "tender" vegetables that must not be planted in the open until there is no danger of frost.

Cucurbitous Or Vine Crops

Cucurbitous Or Vine Crops (Group 9) are "tender" vegetables that require high temperatures and usually a long season, Sandy loams preferred.

Corn, Okra And Martynia

(Group 10.) High temperatures are necessary for the best results. The soil should be moist and fertile.

Perennial Vegetables

The soil should be enriched annually by the application of rotten manure. Nitrogenous fertilizers are especially beneficial.

Although the foregoing method of classification is exceedingly valuable, the requirements of crops, even in the same group, are so variable that a complete discussion of each crop is necessary to give accurate cultural directions. The vegetables are taken up in alphabetical order, because this arrangement makes the book most convenient for reference.