THE ECONOMIC BIOLOGY OF PLANTS 455 



Leaf Food Products. We usually think of leaves as fodder for 

 animals (grass, hay, etc.), but notice the list of those that we 

 commonly use ourselves. We must include the garden vegetables, 

 cabbage, lettuce, celery, spinach, pie plant, parsley, onion, cress; 

 the flavors of. mint and wintergreen; tea and tobacco; and the 

 drugs, cocaine and belladonna. Although leaves have little real 

 nourishment in them because not intended as storage places for 

 food, yet they are necessary to man's diet, since they supply many 

 of the mineral salts, especially iron and potassium compounds, 

 which are essential .to health. 



Flowers. Flowers we seldom eat, but cauliflower is one excep- 

 tion, and cloves and capers are both flower products. 



Fruits. Fruits furnish an extended list of foods for man. We 

 classify them as follows: pomes, such as apples, pears, and quinces; 

 stone fruits, like the peach, plum, cherry, apricot, and prunes; 

 citrus fruits, orange, lemon, grape fruit; simple berries, currant, 

 grape (raisin), blueberry, tomato; compound berries, such as 

 raspberry, strawberry, and blackberry; gourd fruits, pumpkin, 

 squash, cucumber, melon, and citron; miscellaneous, banana, date, 

 olive, peppers, vanilla, allspice. 



Hops and opium are also fruit products and, though not foods, 

 may be mentioned at this point. Like leaves, fruits are not often 

 very concentrated foods, but supply sugar, acids, and mineral 

 salts which are very necessary to a proper diet. 



Foods from the Spore Plants. The spore plants furnish but little 

 toward man's food, mushrooms being the only ones commonly 

 eaten, and of these many are dangerous and the best only one-sixth 

 as rich in proteid as meat. 



Iceland moss is a curious lichen sometimes used in jellies and 

 medicines. Though we do not eat them to any extent we must 

 not forget that we could not do without spore plants, such as yeast 

 and certain bacteria that help in preparing such important foods 

 as bread, butter, and cheese. 



Fiber Plants. Cotton is the most valuable plant fiber; it is an out- 

 growth of the outer coat of the cotton-seed, intended to aid in its 

 dispersal, and consists of strong, twisted fibers very well adapted 



