2 NATURE STUDY AND AGRICULTURE 
Edible Parts of Plants. — All parts of the plant may contain 
nourishment capable of supporting animal life. Horses, 
cattle, sheep, and many other animals may eat the entire 
plant, either green or dried, and ordinarily they eat it in a 
raw state. The human palate and stomach, however, are more 
particular. It is usually necessary to cook food in order to 
develop the flavor and make it more digestible, and generally 
mankind uses for food only a small part of the plant. Ina 
very few instances, as in beet ‘‘ greens,’’ we eat the whole plant ; 
more frequently we eat the leaves, as in case of lettuce and 
cabbage. In many important cases it is the roots that we 
use, as sweet potatoes, carrots, turnips, parsnips, and radishes ; 
while the common white potato is a form of underground stem 
called a tuber. 
It is in the fruit, however, that the plant stores its richest 
food, for that contains the seed upon which it depends for the 
perpetuation of the species. By fruit we mean, here, the 
seeds together with the vessel which contains them. Some- 
times it is the seed-vessel that we prize, as in apples and pears, 
melons and cucumbers, tomatoes and egg plants; but in our 
most important and most nourishing plant foods it is the seeds 
alone that are used. We refer to the cereals (wheat, rye, 
barley, oats, rice, and corn) and the legumes (peas, beans, 
and lentils). These seeds form the staple food of civilized 
man in practically all parts of the world. 
Cultivation and Improvement. — Of the countless number 
and variety of plants which the land produces, many grow 
wild, cared for only by the hand of nature, while others have 
been domesticated and made more or less dependent on the 
care of man. To the latter class people have long given their 
chief attention, for most of our common food plants have been 
under cultivation from ‘prehistoric times. For example, 
