Primary & Middle School Biology · Grades 1–9

16Flowers, Fruits and Seeds

In April the cherry tree is white with blossom; in June it hangs with cherries. Where did the flowers go — and where did the fruit come from? The answer is one of the prettiest transformations in the living world: the flower does not disappear, it becomes the fruit.

16.1 Looking inside a flower

Definition 16.1 (The parts of a flower)

A flower is the part of the plant that will make the seeds. From the outside in:

the petals, colored and scented, which attract visiting insects;
the stamens, thin stalks dusted with pollen, a fine yellow powder;
in the very center, the pistil, a little flask; deep inside it lie the flower’s future seeds.

Inside a flower, cut in half: petals around, pollen-bearing stamens, and the pistil in the center with the future seeds inside.

Example 16.2 (Dissecting a tulip)

Open a wilting tulip gently, petal by petal. Inside stand the stamens — brush one on your finger and it leaves yellow pollen dust — and in the middle the fat green pistil. Slice the pistil across (a grown-up’s knife-work) and there they are: rows of tiny pale future seeds.

16.2 From flower to fruit

Proposition 16.3 (Pollination, then transformation)

For the transformation to start, pollen must reach the pistil — that step is pollination. Bees and other insects do most of the carrying, dusted with pollen as they drink from flower after flower; the wind does some too. After pollination:

the petals and stamens, their work done, wither and fall;
the pistil swells and becomes the fruit;
the future seeds inside it become the seeds.

A fruit is a transformed pistil, and every true fruit carries seeds.

Proof. Admitted at this level. ∎

Example 16.4 (Watching one cherry happen)

Follow a single cherry blossom. April: white petals, buzzing bees. May: petals snowing down; where each flower stood, a tiny green ball — the swelling pistil. June: the ball grown red and sweet — a cherry, with the stone (its seed) inside. The flower did not fall; only its petals did.

Remark 16.5 (No bees, no cherries)

Cherry growers welcome beekeepers’ hives into their orchards — without insect visits, most blossoms would stay unpollinated and fall without ever becoming fruit. The bee is not stealing from the flower; flower and bee feed each other: nectar for the bee, pollen delivery for the plant.

Pollination in progress: a bee deep in a cherry blossom, dusted with the pollen it will deliver to the next flower.

16.3 Fruit or not fruit?

Method 16.6 (The seed test)

To decide whether something from the greengrocer is a fruit in the biologist’s sense:

cut it open;
look for seeds (or a stone, which is a seed in a hard shell);
seeds inside — it grew from a flower’s pistil: a fruit. No seeds anywhere — it is another part of the plant: root, stem or leaf.

Example 16.7 (Surprises at the greengrocer’s)

The seed test springs surprises. Tomato: full of seeds — a fruit, whatever the salad bowl says. Cucumber and courgette: seeds — fruits. Green bean pod: seeds in a row — a fruit. Carrot: no seeds — a root (Exercise 3.10 guessed it). Lettuce: no seeds — leaves. Potato: no seeds — a swollen underground stem.

Remark 16.8 (Kitchen words, science words)

In the kitchen, “fruit” means sweet and “vegetable” means savory — useful for planning dessert, useless for biology. The biologist’s word follows the seed test. Both vocabularies are fine, as long as you know which one you are speaking.

16.4 Exercises

Exercise 16.1 ★

Name the parts of a flower from the outside in, with each part’s job.

Solution

Solution of Exercise 16.1.

Petals (colored and scented, they attract insects); stamens (thin stalks carrying pollen); the pistil in the center (the little flask holding the future seeds).

Exercise 16.2 ★

What is pollen, and where is it found? What is pollination?

Solution

Solution of Exercise 16.2.

Pollen is the fine yellow powder carried by the stamens. Pollination is pollen reaching the pistil — mostly delivered by visiting insects, sometimes by the wind.

Exercise 16.3 ★

After pollination, what becomes of: (a) the petals? (b) the pistil? (c) the future seeds inside it?

Solution

Solution of Exercise 16.3.

(a) They wither and fall. (b) It swells and becomes the fruit. (c) They become the seeds inside the fruit.

Exercise 16.4 ★

Retell the story of one cherry, from white blossom to red fruit, in three dated steps.

Solution

Solution of Exercise 16.4.

April: white blossom, bees visiting — pollination. May: petals fall; the pistil of each pollinated flower swells into a tiny green ball. June: the ball has grown into a red, sweet cherry with the stone — the seed — inside.

Exercise 16.5 ★

Why do cherry growers welcome beehives in the orchard?

Solution

Solution of Exercise 16.5.

Because without insect visits most blossoms are never pollinated, and an unpollinated flower falls without becoming fruit. The bees’ pollen deliveries are what turn blossom into cherries.

Exercise 16.6 ★

State the seed test, and apply it to the tomato and the carrot.

Solution

Solution of Exercise 16.6.

Cut it open and look for seeds: seeds inside means it grew from a pistil — a fruit; none means another plant part. The tomato is full of seeds: a fruit. The carrot has none: not a fruit but a root.

Exercise 16.7 ★

Fruit or not, by the seed test: the cucumber, the lettuce, the green bean pod, the potato?

Solution

Solution of Exercise 16.7.

Cucumber: seeds — fruit. Lettuce: no seeds — leaves, not a fruit. Green bean pod: a row of seeds — fruit. Potato: no seeds — a swollen underground stem, not a fruit.

Exercise 16.8 ★

Try it: at home, cut open three things from the kitchen and run the seed test on each. Which surprised you?

Solution

Solution of Exercise 16.8.

Open answer. The usual surprises: tomato, cucumber and bean pod turning out to be fruits; the strawberry carrying its tiny seeds on the outside.

Exercise 16.9 ★★

A late frost kills all the blossom on the plum tree in April. What will the June harvest be, and why? Use Proposition 16.3.

Solution

Solution of Exercise 16.9.

Almost no plums. Fruit can only come from a pollinated flower’s pistil; with the blossom dead in April, there is nothing left to transform, however fine the summer.

Exercise 16.10 ★★

“The apple grows so that we have something nice to eat.” What is the apple really for, from the apple tree’s point of view? What lies at its core, and what could each one become? (Recall Chapter 9.)

Solution

Solution of Exercise 16.10.

For the tree, the apple is a way of making and protecting seeds. At its core lie the pips — seeds — and each pip, planted, could germinate into a new apple tree. That we find the packaging delicious is our luck (and, for the tree, a way of getting its seeds carried far from home).

Terms defined in this chapter

The parts of a flower

See all 479 terms in the glossary