SEED-BEARING PLANTS 
493 
the plant families. Here belong the "grains " (wheat, rice, 
oats, barley, rye, corn, and others) which furnish the most 
important vegetable foods of the entire human race. The 
commercial grains have been cultivated so long by man 
FIG. 377. Water plantain (Alisma Plantago-aquatica) . 
that their origin is shrouded in mystery, antedating, as it 
does, the dawn of written history. Except the bamboos, 
which are shrubs or trees, the grasses are all herbaceous. 
The chief characteristics of the family are that the fruit 
is always a grain or caryopsis. 1 The seed invariably con- 
1 A one-seeded, seed-like fruit, with the wall of the ovary (pericarp) 
united closely (adnaU) to the seed within. 
