All trees produce seeds so that new trees, seedlings, can grow. Trees that produce flowers and protect their seeds inside a casing are called angiosperms (i.e., oaks, maples, cherry trees, dogwoods). These flowers attract insects (especially bees), birds, and bats to assist with their pollination by producing colorful petals and an aromatic scent. The pollinating animals head into the center of the flower, often following a colorful pattern down the center of the petals called a honey guide (think of them as landing lights on an airport runway), in search of nectar. Pollen from the stamen (male part) of the flower attaches to the animal’s body and is transferred to other flowers as the animal makes its way from tree to tree. The pollen is transferred to other flowers when grains brush onto the tips of the pistils. When pollen brushes onto the pistil, pollination occurs. A special tube then grows, and the pollen grains travel down the tube into the flower where the seeds will grow inside the female part called the ovary. Once the pollen grains enter the ovary, fertilization occurs and seeds develop.

Many trees, however, do not have the traditional flowers. Numerous trees are gymnosperms, which mean they produce "naked" seeds not enclosed in a casing. In the case of trees with catkins such as the birch, willow, hickory, and conifers, wind is a key pollinator. One catkin can produce up to 5,500,000 pollen grains so that it stands a chance of having some of its pollen blown by the wind to the female flowers.

Dissecting A Flower

Indoor Any Season

Objective: To help students understand the basic parts of tree flowers and their role in pollination.

You'll need:

Use the Treeture, Blossom, as a guide, icon or symbol to help animate and enhance your pollination lesson. Blossom is a Treeture Tree Twirler who helps the wind spread tree pollen and encourages pollinating insects to do their jobs so that baby trees can be born. She loves all of the beautiful tree flowers and is very busy every spring making sure pollination is occurring. Briefly discuss that pollination and fertilization are the processes that must occur in order for flowers to produce new seeds that will eventually grow into new tree seedlings. In order to understand the processes of pollination and fertilization, students must first recognize all of the parts and functions of a flower.

  • Break students into small groups and give each group a flower, tweezers, and a flower structure worksheet. Explain this is not a tree flower, but it is very similar to many tree flowers.
  • Ask students to identify the petals on the flower and explain their function. Color, smell, and shape are all important in attracting pollinating insects. Flower petals are often very colorful (That is why bees sometimes are mistakenly attracted to artificial flowers on women’s hats etc.!). Also add that many have honey guides (markings) to direct insects to the sweet nectar which gives them energy to continue their pollinating job.
    Gently pull off the petals, observe and smell them. Have students complete the petal and nectar sections of their charts.
  • Ask students if they can identify the stamens in the flower. The stamen is the male portion of the flower and produces the pollen. Remove the stamens and complete charts for stamen and pollen.
  • Identify the pistil in the center of the flower. The pistil is the home of the female part of the flower. The pollen the insects gathered on their legs and bodies from the stamen of a different flower or tree is rubbed onto the tip of the pistil. Explain that at the bottom of the pistil sits the ovary where an egg is waiting to be fertilized by a pollen grain. Once the pollen fertilizes the egg, seeds are produced. Remove the pistil and complete charts for pistil and ovary.

Ask students why some trees produce flowers to see what they have learned. You may want to branch out into a discussion of trees that do not produce true flowers. These are the trees Blossom loves best because she can dance and twirl to help the wind pollinate the catkins. The spring would be a great time to observe local trees and observe whether they produce true flowers or catkins. You could keep a list of the types of trees, the types of flowers they produce, and how their new seeds are housed. Investigate to see how they are typically pollinated. Regardless of whether a tree produces true flowers or catkins, after pollination and fertilization, the tree will produce seeds.

Get Flower Structure Worksheet