flowers. From what you have observed, make up a definition of a pepo fruit. Draw a cross section of the squash, natural size.

BERRY A gardener or vegetable vender rarely calls a tomato a berry. Tomatoes, however, are considered excellent examples of this type of fruit. In botanical language, a berry is any pulpy, juicy mass containing seeds, this mass inclosed in a rather tough but thin covering, as a rind or skin. In popular language, a berry is any small round edible fruit containing small seeds.

DRUPE. Another fleshy fruit is the drupe or stone fruit. This is illustrated by the peach or cherry. In the drupe a juicy interior is surrounded by a skin; the center of the fruit is occupied by a stone which contains the seed. This stony covering is made up of the inner wall of the pericarp (ovary wall) which has separated from the part which forms the flesh of the fruit. The connection between these two layers is well seen in a clingstone peach or a very young cherry.

Classify as many of the following named fruits as you can: plum, apricot, egg plant, watermelon, lemon, pomegranate, cranberry, black haw, pear, date, olive. Make up your classification in tabular form.

Dry Fruits. A dry fruit may split open to allow the escape of seeds. The pea is an example. Such a fruit is said to be dehiscent." Study an open pea pod. When it splits, it separates along both edges of the two sides or valves. Such a fruit is called a legume.

Follicle. If the ovary splits along one edge of a valve only, the fruit is called a follicle. The milkweed pod is an example. Capsule. When the ovary forming the fruit is compound, the ovary having several locules, it is said to be a capsule.

1 For laboratory work on the tomato, see Hunter and Valentine, Manual, page 71. 2 For laboratory exercises on dry dehiscent fruits, see Hunter and Valentine, Manual, pages 66, 67, 68.

Examine a capsule of Jimson weed. Cut a cross section and decide how many locules there are. Where is the placenta? How many do you find? Open a green fruit to see the number of seeds produced. Draw the

Indehiscent Fruits.

SILIQUE. - Attention is called to the two or three odd types of capsule frequently seen. All flowers belonging to the mustard family form a silique. This differs from a legume in the presence of a false partition which divides the interior into two parts. Another common form is the purse-shaped capsule; it is known as silicle, best seen in the fruit of the peppergrass or of the shepherd's purse.

Among those of most importance to man economically are the dry indehiscent fruits. Such fruits do not

Among them are found the
Many of our most destruc-

open to allow the escape of seeds. grains, such as wheat, oats, and corn. tive weeds bear indehiscent dry fruits.

ACHENE.

- The simplest and commonest of all indehiscent fruits is the achene. This we have seen before in the buttercup and on the outside of the strawberry. In many flowers, especially those of the great composite family (a group of plants containing many of the most noxious weeds, as the thistle, dandelion, sneezeweed, and others), hairlike projections are developed from the upper part of the fruit.

Cross section of a pecan nut.

The acorn, a nut in which the involucre only partly covers the fruit.

These projections (collectively called the pappus) are of use to the fruit because they aid in carrying it to other localities at some distance from the parent plant.

NUT. A nut can usually be recognized by the hard pericarp, or ovary wall, which fits tightly over the kernel. The latter, with its covering, is the true seed. The acorn and pecan are good examples of nuts. The Brazil nut is

another example of a seed commonly called a nut. We have to bear in mind the distinction between true nuts and hard seeds. An example of the latter is the horse-chestnut. Here the whole capsulelike structure is the fruit and the "nuts" are hardcoated seeds. On the other hand, the acorn cup is made up of leaflike structures which together form what is called an involucre. The chestnut bur is another example of the involucre which has become prickly, the nuts being each a true fruit.

GRAIN. The grain, as we shall see when we study the corn more carefully, is a fruit in which the seed occupies most of the space within the fruit, and the seed coat has become so closely attached to the ovary wall that the two coats cannot be separated.

KEY FRUIT OR SAMARA. A very common indehiscent fruit is found on the maple, ash, elm, and other trees. It is the key fruit or samara. In this

Grain; spikes of ripened flowers.

Distinction between Seeds and Fruits. - We have seen that in the case of one-seeded fruits it is sometimes difficult to distinguish between the seed and the fruit. If we are able to examine the flower which forms a certain fruit, we ought to have no difficulty in making out all of its parts. A cross section through the ovary will show us that seeds are always surrounded not only by seed coverings, but also by the ovary wall, which later forms the pericarp. In

1 For laboratory exercises on dry indehiscent fruits, see Hunter and Valentine, Manual, pages 69, 70, 74, 75.

dehiscent fruits the distinction between seed and fruit is always easy. In the indehiscent fruits it is not always so plain, especially in the nuts, grains, and the achene fruits. In all of the above fruits it is necessary to remember that the pericarp, or ovary wall, adheres quite closely to the seed coat. In a grain of wheat the two have actually grown together. In a nut it is always possible to scrape off the seed coat, as a thin brownish covering around the kernel of the nut. Try this with a chestnut.

- In the acorn,

Homology of Parts in Flowers and Fruits. chestnut, and hazelnut a number of leaflike structures come out on the branch just under the fruit and become the capsule of the acorn, the bur of the chestnut, and the husk of the hazelnut respectively. All these structures originate from the same place on the branch. Very early in their growth they appear to be leaflike. We have reason to believe that these structures are entirely similar to leaves in structure and position. Any part of a plant or animal that has the same position and structure as another similar part on another plant or animal is said to be homologous with it.

HOMOLOGY OF THE PARTS OF A FLOWER. It is believed by botanists that all parts of a flower (sepals, petals, stamens, and carpels) are homologous to each other and also to leaves. It would not take a great stretch of the imagination for you to see how like leaves are the sepals and even the petals of some flowers.

Horizontal diagram of a lily. The central area represents the Ovary; the bean shaped structures, the stamens; and the two outer cir

men.

In roses and in the water lily the petals become thinner as we go inward and become tipped with yellow. On examination, this yellow tip is seen to be a pollen box. In short, the petal has become a staA very good imitation of a pea pod could be made by folding a pea leaflet along the midrib. In the Sedum previously studied it will be seen that the carpels bear the same relation to the stamens as the stamens do to the petals. This holds true of petals and sepals. In other words, in a flower each part in each circle or whorl of parts alternates with the parts of the next succeeding whorl. A glance at the diagram will make this more clear. If each of the parts is homologous to leaves, then an opened bud ought to help make this plain.

cles the petals and sepals, respectively.

It becomes very evident after we have studied a number of flowers and have then taken up the fruits, that the same part of the flower almost invariably appears as a certain part of the fruit, although the part may serve a very different purpose in the different fruits. We have already referred to some examples of this. Take as another example the fate of the ovary wall or pericarp in such fruits as the peach, the apple, the pea, the nut, and a key fruit of maple. In all the above the pericarp of one

Young cedars around parent tree. Photographed by Overton.

is homologous with the pericarp in another. Yet what a contrast between the papery core of the apple and the hard shell of the nut, the partly fleshy and partly hard pericarp of the peach and the outgrowth we call the wing of the key fruit.1

Seed Dispersal. If you will go out any fall afternoon into the fields, a city park, or even a vacant lot, you can hardly escape seeing how seeds are scattered by the parent plants and trees. If you count the young maple seedlings which

1 The teacher should point out other homologies in flowers and fruits. This field is one of the richest in this respect in all the field of botany and zoology. 2 At this point a field trip may well be taken with a view to finding out how the common fall weeds scatter their seeds. Fruits and seeds obtained upon this trip will make a basis for laboratory work on the adaptations of seed and fruit for dispersal.