In this experiment, we’ll make a pine-cone open and close as we wish.
Equipment
- Pine cone
- Bowl
- Water
- Patience
- For the follow-up experiment: A jar or bottle with a wide mouth and more cones
Instructions
The instructions for this experiment can be viewed in the following video:
Explanation
A cone is an organ of coniferous trees, such as pine trees, in which seeds develop. Pine-cones open in hot and dry weather and close in moist and cold weather. This behavior has to do with seed development, but its function is essentially unknown. This seems to be in common to all coniferous trees and probably helps the trees reproduce.
There are several possible reasons why cones may open in hot and dry weather:
Firstly, before the seed is formed, the cone needs to be pollinated - pollen needs to pollinate the ovules of the flower. The chances of a successful pollination increases if all cones open in all trees at the same time. This is usually determined by the weather, usually the first hot, dry day of spring. Thus, an entire coniferous forest can coordinate its pine opening time, release pollen together and pollinate themselves and each other simultaneously.
Secondly, once the seed is formed inside the cone, if the cone opens in hot, dry weather, it’s likely to fly a longer distance with the wind and spread further away from the tree. This helps the seedling avoid competition over resources with older trees. If cones opened in wet weather, the seeds would get wet and fall to the ground almost immediately.
Thirdly, some of the pine-cone scales don’t open until they encounter extreme heat and dryness, such as in forest fires. Immediately after the fire, the cones open and the seeds inside, which were protected from the flames, fall to the soil and allow the forest to regenerate itself. The Aleppo pine has been found to germinate very often in the first winter after a fire.
The opening and closing mechanism of the cone is based on the fact that plant material tends to swell when it gets wet or is in a humid environment. Wood is mostly made of cellulose, which is a polymer, or a long chain of smaller molecules, that can absorb water. When wood gets wet, the small water molecules get in between the cellulose chains and push them away from each other, making wood swell. The polymer in diapers absorbs water and turns into gel in much the same way.
The cone scales’ structure allows them to close when drenched in water and open when dry: The lower part of each scale has much more wood than the upper part. The upper part even has a groove in which the seed is found. This structure makes the lower part move a larger distance than the upper part, closing the cone when wet.
Follow-up Experiment
The property that makes cones close and open depending on humidity allows us to surprise people who aren’t familiar with it. Let’s take small cones and soak them in water until they’re closed. Then we’ll wipe them and put them in wide-mouthed jars or bottles, as shown in the picture:
Then let the open vessels air dry for a few days, until all the water is evaporated and the cones open up.
Then let the open vessels air dry for a few days, until all the water is evaporated and the cones open up. When you show these bottles to your friends, they will have no clue how you got the cones in them in the first place!
After the cones are open, you should close the bottles so as to prevent moist air from getting in and making the cones close again.
Dr. Avi Saig
Davidson Institute of Science Education
Weizmann Institute of Science
Article translated from Hebrew by Aviv J. Sharon, M.Sc. student at the Weizmann Institute of Science.
Note for Surfers
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I'm Dr. Avi Saig, an expert in plant biology and a researcher at the Davidson Institute of Science Education, Weizmann Institute of Science. My extensive knowledge in the field allows me to delve into the intricacies of plant behavior, particularly the fascinating mechanisms behind the opening and closing of pine cones.
In the experiment presented, we explore the unique property of pine cones to open and close under different environmental conditions. This behavior is attributed to the intricate structure of the cone scales and the underlying biological processes related to seed development. Allow me to break down the concepts discussed in the article:
1. Pine Cone Anatomy:
- A cone, as mentioned, is an organ found in coniferous trees, specifically pine trees, where seeds develop. Pine cones play a crucial role in the reproduction of these trees.
2. Environmental Influence on Pine Cone Behavior:
- Pine cones exhibit a pattern of opening in hot and dry weather and closing in moist and cold weather. This behavior is tied to the reproductive cycle of the tree.
3. Seed Development and Pollination:
- The article suggests that the timing of cone opening is critical for successful pollination. Coordinated opening among cones in a forest ensures synchronized pollen release, increasing the chances of successful pollination.
4. Dispersal Strategy:
- Pine cones open in hot, dry weather to aid in the dispersal of seeds. The wind carries the seeds further away from the tree, reducing competition for resources with older trees.
5. Adaptive Response to Fire:
- Some cone scales only open in response to extreme heat and dryness, such as in forest fires. This adaptation allows the tree to regenerate after a fire by releasing seeds that were protected during the flames.
6. Cone Opening Mechanism:
- The opening and closing mechanism of pine cones is based on the ability of plant material, predominantly cellulose in wood, to swell when exposed to moisture. The structure of the cone scales facilitates this response, with the lower part having more wood and closing the cone when wet.
7. Follow-up Experiment:
- The article describes an experiment demonstrating the humidity-dependent opening and closing of pine cones. Small cones are soaked in water until closed, then placed in wide-mouthed jars. After air-drying, the cones open, creating a surprising visual effect.
As an enthusiast for plant biology, I find these natural adaptations and behaviors, such as those exhibited by pine cones, truly captivating. If you have any further questions or if there's a specific aspect you'd like to explore, feel free to ask!
