THE INTER-RELATIONS OF PLANTS AND MAN 119 



getting dinner. Less frequent is the storage of food in stems and 

 leaves. The underground stem of the white potato is the most 

 important edible stem; other edible stems and leaf bases include 

 celery, rhubarb and asparagus. Leaves, being short-lived struc- 

 tures, are rarely used as food storage organs; but though low in 

 nutrient value, they are prized as vegetables because of their 

 crisp succulence and high vitamin and mineral content. Edible 

 leaves or buds include spinach, water cress, cabbage, lettuce and 

 onion. 



The reproductive process in seed plants has resulted in organs 

 of great significance as foods. Gymnosperms have no fruits, but 

 their seeds are in many cases tasty and edible. The seeds of the 

 pinon and other pine species are known as pine nuts; they have 

 been eaten for centuries by the Indian and Mexican population 

 of our Southwest, who also grind them into a meal. Angiosperms, 

 chiefly because of their fruit habit, are of much greater food 

 importance. Popularly known as vegetables are such fleshy fruits 

 as tomatoes, peppers, ^gg plant, squash and cucumber; while 

 fruits in both the botanical and popular sense include the various 

 berries, grapes, melons, apples, pears, plums, cherries, peaches, 

 citrus fruits and numerous tropical species including pineapples, 

 bananas, figs and dates. Seeds often constitute the most nutritious 

 part of a fruit, as in the nuts and the cereal grains. In the legumes 

 (peas and beans) the p>od, which is the fruit, is sometimes eaten 

 with the seeds, though the latter possess most of the stored food in 

 their fleshy cotyledons. Only a few flowers are used as foods, most 

 familiar being the artichoke and the cauliflower. 



The importance of plants as foods constitutes the subject 

 matter of the chapters in Part Two, where also are considered 

 those substances found in plants which are necessary food ad- 

 juncts: the sugars produced in the sugar cane and sugar beet; the 

 stimulants found in the coflee, tea and cacao plants; and the 

 spices secured from a great variety of plant species. 



Other ways in which plants and man have formed inseparable 

 associations have been the outgrowth of human needs and desires 

 above those of our animal relatives. Some of these relations de- 

 pend upon the presence of fibers or other supporting tissues. 

 Various kinds of strengthening fiber cells, chiefly developed in 



