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Gymnosperms: Pine Cone Experiment

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Author: Tricia Edgar

Pine cones, fir cones, spruce cones: if you live in a cool climate, you’ll see these seed-bearing structures all over the parks and the roads. Why do trees make cones? They’re the places where trees make and keep their seeds. In this investigation, you’ll explore the different properties of pinecones and discover how they can grow new trees and help you tell the weather!

Problem: How do pine cones make more trees?

Materials

  • Several pine cones
  • Spray bottle
  • Pan
  • Water
  • Ruler
  • Washcloth
  • Magnifying glass

Procedure

  1. Find a pine cone that’s tightly closed. Bring it inside and let it sit in a warm, dry place for several days. This should cause the cone to open and be ready to release its seeds.
  2. To help the cone release the seeds, bang it on a flat, hard surface. If the cone is quite dry, the seeds will begin to fall out. If they do not, place a washcloth or gloves on your hand and twist the cone as if you were wringing out a washcloth. The cone should crack gently. Look into the middle of the cone and you will see thin, flat scales. These are the seed-bearing parts or ovulate scales.
  3. Remove one or two seeds that look like they are intact, and look at them under your magnifying glass. Can you see two wings on the scale? Each seed has a wing-like part that helps it move in the wind. Can you see the seed on the bottom of the wing? Why is it located there?
  4. Now, take another dry cone and place it in a pan of water. Place another cone next to the pan of water. Leave them there overnight. What happens to the cones?
  5. Finally, place several cones outdoors. Use your ruler to measure the openings of the scales on the cone. Are there days when they are very open? Completely closed? Track the humidity on the weather report and create a graph that shows humidity on the side and the size of the scale openings on the bottom. What do you find?

Results

When the cone gets damp, it will close up.

Why?

There are many kinds of coniferous trees in the world, and these trees cover huge areas of land, particularly in the northern parts of the world. Conifers include spruces, pines, hemlocks, cedars, and many more species of trees. They generally grow in cool climates and have thin, needle-like leaves.

Most species of conifers are evergreen. This means that they don’t lose all of their leaves in the fall like many deciduous plants do. Deciduous plants generally lose their leaves when a cold or dry season is approaching. That way, they can slow down and stop growing for a while when times are hard. Coniferous trees are different. They don’t lose their leaves at one time. Instead, they lose them gradually over time. However, there are exceptions. The larch is one conifer that loses its needles in the fall.

What makes a conifer a conifer? These trees are called conifers because they have a certain structure that holds their seeds. This structure is called a cone. Conifers are called gymnosperms. Gymnosperms have naked seeds! Their seeds are not inside a protective house like those of an angiosperm, or flowering plant. The seeds of a gymnosperm are more exposed.

Like many plants, coniferous trees use sexual reproduction to create seeds that will make new trees. Sexual reproduction is when plants or animals use genes from a male and a female to create seeds that have genes from both. To do this, coniferous trees have seed cones and pollen cones. The seed cones are what you might normally call a cone: they are often brown, with woody scales that have seeds inside them. The pollen cones are generally smaller and squishier. They send out the pollen that containers sperm cells. The sperm cells fertilize the seed cones and help them make new seeds.

One intriguing feature of conifers is the fact that they’re hygroscopic. This means that they absorb or bring in moisture from the air. When it is damp in the air, a conifer’s cone gets damp. The cells on bottom of each seed-bearing scale absorb water and this pressure makes the scale fold forward, closing up the cone. When the weather is warm and dry and it’s easy for seeds to crack out of the cone and get moved around, the scale opens up. You’ll find that cones close when it’s rainy, but they also close up when it’s humid, or damp in the air.

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