Monocots

1. Seed with two cotyledons (seed leaves)

2. Flower parts mostly in fours or fives or multiples of four or five

3. Leaf with a distinct network of primary veins

4. Vascular cambium, and frequently cork cambium, present

5. Vascular bundles of stem in a ring

6. Pollen grains mostly with three apertures (thin areas in the wall—see Figures 23.6 and 23.7)

1. Seed with one cotyledon (seed leaf)

2. Flower parts in threes or multiples of three

3. Leaf with more or less parallel primary veins

4. Vascular cambium and cork cambium absent

5. Vascular bundles of stem scattered

6. Pollen grains mostly with one aperture stamen —

anther -filament -

ft 1

petal -

(petals = corolla)

ovule -

mm receptacle stigma style

- ovary pistil peduncle ■

Figure 8.5 Parts of a generalized flower. The interior structure of the ovule and the sexual processes involved are discussed in Chapter 23.

Figure 8.6 A flower of jimson weed (Datura). The petals are united in a single, flared sheet of tissue.

other tissues) of a flower will develop into a fruit. If at least a few of the ovules are not fertilized, the flower normally withers and drops without developing further. Pollen grains contain specific stimulants called hormones (discussed in detail in Chapter 11) that may initiate fruit development, and sometimes a little dead pollen is all that is needed to stimulate an ovary into becoming a fruit. It is the hormones produced by the developing seeds, however, that promote the greatest fruit growth. These hormones, in turn, stimulate the production of more fruit growth hormones by the ovary wall. In a few instances (e.g., the cultivated banana), fruits develop without fertilization. Such development is called parthenocarpic. Parthenocarpy is discussed in Chapter 23.

Fruit Regions

Most of a mature fruit has three regions, which sometimes merge and can be difficult to distinguish from one another (Fig. 8.8). The skin forms the exocarp, while the inner

Chapter 8

panicle

Chapter 8

panicle

Alnus Dichasium

Catkin

Alder Alnus sp.

Elephant heads Pedicularis sp.

Tansy

Rudbeckia sp. Water hemlock catkin catkin m

Catkin

Alder Alnus sp.

False Solomon's seal Smilacina racemosa

Elephant heads Pedicularis sp.

False Solomon's seal Smilacina racemosa

Spike

Fireweed

Spike

Fireweed

Tansy

Garden geranium Pelagonium sp.

Tanacetum vulgare

Corymb

Epilobium angustifolium

Coneflower

Rudbeckia sp. Water hemlock

Cicuta sp.

Dichasium Weeds

dichasium

Q oXo dichasium

Cicuta sp.

Compound Umbel Plants
compound umbel

Figure 8.7 Inflorescence types. Each ball represents a flower. In all inflorescences shown, except for the dichasium and catkin, the lowermost or outermost flowers open first. The flowers then open in succession upward or inward. In a dichasium, the central flower opens first, and the side flowers open simultaneously. In a catkin, all the flowers open simultaneously. (From Moore, Clark, and Vodopich, Botany, 2nd edition. © 1998 The McGraw-Hill Companies. All rights reserved.)

Peach Skin Mesocarp Endocarp Seed

seed endocarp mesocarp exocarp

Figure 8.8 Regions of a mature peach.

seed endocarp mesocarp exocarp

- pericarp

Figure 8.8 Regions of a mature peach.

boundary around the seed(s) forms the endocarp. The endo-carp may be hard and stony (as in a peach pit around the seed). It also may be papery (as in apples), or it may not be distinct from the mesocarp, which is the often fleshy tissue between the exocarp and the endocarp. The three regions collectively are called the pericarp. In dry fruits, the pericarp is usually quite thin.

Some fruits consist of only the ovary and its seeds. Others have adjacent flower parts, such as the receptacle or calyx fused to the ovary or different parts modified in various ways. Fruits may be either fleshy or dry at maturity, and they may split, exposing the seeds, or no split may occur. They may be derived from a single ovary or from more than one. Traditionally, all these features have been used to classify fruits, but unfortunately, not all fruits lend themselves to neat pigeonholing by such characteristics. Some of these problems are pointed out in the classification that follows.

Kinds of Fruits

Fleshy Fruits

Fruits whose mesocarp is at least partly fleshy at maturity are classified as fleshy fruits.

Simple Fleshy Fruits Simple fleshy fruits develop from a flower with a single pistil. The ovary may be superior or inferior, and it may be simple (derived from a single modified leaf called a carpel), or it may consist of two or more carpels and be compound (for a discussion of the derivation

Fertilisation Flowering Plants Images

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