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Botany Basics: What's In a Flower?

This is the first in a series of three articles on some botany concepts. Watch out for upcoming articles on "What's in a Fruit" and "What's in a Seed." For more information about these and other topics, visit www.seeds.ca/saveyourseeds.


The purpose of every flower is to fertilize each seed with a grain of pollen.

Pollen is made on anthers, which are the male part of the plant. It is then collected on the stigma, which is the female part of the plant. During fertilization, pollen travels down tubes to an ovary that later grows into a fruit. Each grain of pollen fertilizes one seed, and genetically, the baby plant in the seed is half of the plant that made the pollen, and half of the plant that made the fruit.

Flowers are categorized under four types. Most plants have a combination of these types. Some plants, for example, have complete and closed flowers. Others may have complete and open flowers, or incomplete and open flowers.

 

 

Complete

Incomplete

  

Open

Closed

Each flower has both male and female parts

Each flower is either male or female.

 

Flower shape allows insects to reach the pollen and carry pollen from flower to flower.

Flower shape blocks insects from reaching the pollen.

Each flower makes pollen, and also makes fruit.

Some only make pollen; some only make fruit.

 

This kind of flower is cross-pollinating.

Since pollen stays within the flower, this kind of flower is self-pollinating.

May be open or closed

Always open, so that they can be cross-pollinated

 

Can be complete or incomplete.

Always complete, so they can self-pollinate.

 

Here are examples of how flowers from some common garden vegetables work.
(Click on the pictures to magnify them).

 

Tomato

Closed, Complete, Self-pollinating

Tomato flowers are almost always self-pollinating. This means pollination almost always happens inside each flower. Bees can’t enter the closed flowers, so they don’t generally cross-pollinate different varieties nearby. Pollen is made on the inside of the cone of anthers and collects on the stigma inside the cone.

Bean

Closed, Complete, Self-Pollinating

Like the tomato, beans are self-pollinating. The anthers and stigma are both closed within a coil-like structure, so pollination takes place within each flower. Each grain of pollen fertilizes one seed and this ovary grows into a bean pod. The anthers and stigma in a bean flower are wrapped within a “snail shell.”

Pepper

Open, Complete, Cross-pollinating/Self-pollinating

Since they are in the same family, the pepper and tomato flowers look similar. The pepper flower is complete, but the anthers don’t make a cone, so insects can enter. Pollen is made on the inside of the anthers. As insects move, they brush pollen onto the stigma, so some seeds are self-pollinated. They also carry pollen from flower to flower, so some seeds are cross-pollinated. Each grain of pollen fertilizes one seed, and the ovary grows into a pepper.

Corn

Open, Incomplete, Cross-pollinating (by wind)

Corn plants have male flowers (tassels) at the tops and female flowers (ears) along the stem, so they cannot self-pollinate. The tassels make light pollen which is blown by the wind, then settles on the silks (stigmas). Corn pollen is small and dusty enough to be carried for great distances by wind, so different varieties must be grown far apart to prevent crossing.  Each grain of pollen fertilizes one kernel.

Squash

Open, Incomplete, Cross-pollinating

Squash flowers are either male or female, so they rely on insects to carry pollen. The female flowers only make fruit, and the male flowers only make pollen. Since the flowers cannot self-pollinate, they must be separated by a large distance from other varieties to prevent cross-pollination. Insects carry pollen to the female flowers, where each grain fertilizes one seed.

For more botany basics, information about pollinators, and detailed information about how to save seeds from the vegetables in your garden, check out our new and updated guide, How To Save Your Own Seeds. The book includes cutting-edge information, step-by-step instructions, detailed illustrations, photographs and handy reference charts. For more information or to order your copy, visit www.seeds.ca/saveyourseeds.

 

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