58 SEEDS AND FRUITS 
thin covering, which is usually tightly pressed against the inner 
side of the ovary wall. 
In general structure seeds are similar, all having an embryo, 
stored food, and seed coat, but in size, shape, and in features 
which pertain to the structure of the embryo, composition of the 
stored food, and character of the seed coat, seeds vary widely 
and can be used in many ways by man. The number of coty- 
ledons developed by the embryo is used as a basis upon which to 
classify the Flowering Plants into two classes, Monocotyledons 
and Dicotyledons. From the stored food, whether stored as 
endosperm or in the embryo, various valuable products, such as 
starch, protein, fats and oils, are obtained; and from the hair- 
like outgrowth of the seed coat, as in case of Cotton, various fiber 
products are made. Although seeds may be’ divided into many 
types on the basis of their structure and external features, only 
those types which include the most common seeds will be studied 
in this presentation. 
Bean Type of Seeds. — Of this type of seeds, those of the 
Bean, Pea, Peanut, Clover, Vetch, Alfalfa, Cotton, Pumpkin, 
Squash, Melon, Apple, Peach, Oak, Hickory, and Walnut are ex- 
amples. The type is so named because it is characteristic of the 
Bean family (Leguminosae), a family notable for its many valu- 
able cultivated forms among which are Clover, Alfalfa, Beans, 
Peas, Vetch, and Peanuts. The type is also characteristic of the 
Rose family (Rosaceae), the family to which most fruits, such as 
the Apple, Peach, Pear, Cherry, etc. belong. In this family, 
however, it is the fruit (rarely the seed) that is important. 
The seeds of the Bean type are common to a number of 
plant families and to species and varieties of plants so numer- 
ous that a list naming them all would require a page or more. 
Although many are valuable commercial seeds, some are borne 
by weeds and hence of interest because of their undesirable 
features. 
These seeds differ from other types in having little or no endo- 
sperm. As the seed develops, all or almost all of the food tis- 
sue formed by the endosperm nucleus and adjacent cytoplasm 
is absorbed by the embryo where it is stored in the cotyledons, 
which, consequently, are so much enlarged that they are much 
the largest part of the embryo. (Fig. 63.) For this reason 
these seeds are called exalbuminous seeds, that is, seeds without 
