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Flower Biology

 
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Of what value are flower petals to the plant? Of course, they are pretty to us people, and thus make us want to propagate the plants so that we have more blooms to enjoy. But flowers and their petals were around long before people, and even today bloom in places rarely seen by humans. To continue to exist, petals must provide their host plants with an advantage. What might that be?

One thing we can generally accept is that petals are on flowers that require cross-pollenation by insects or birds. Flowers that are pollentated by the wind are generally small, and without petals. For this reason, one of our starting hypotheses is that petals are there to attract the pollenators - or possibly to indicate the state of fertility of the flower. How can we test this hypothesis?

One human attribute required for this test is patience. Preferably, you should find a patch of many identical flowers that are being "visited" by many bees at the same time. All these visitors will allow you to have less patience as your observations can be made over a shorter period of time. You see, what you need to do is determine the average number of visits per hour for each flower-type. In your patch you have made various flower-types by altering them in various ways, as indicated by the four types shown to the right of the title, above. You can undoubtedly think of other possible alterations, but keep them simple since you might have to alter many flowers.

It is probably well at this point to explain how to move about in the patch of flowers while many bees are buzzing around. Here are a few rules:

• Move SLOWLY
• Look before you grab - make sure a bee isn't in the flower
• Remember that bumblebees are not bees! They are wasps and can sting much more severely.
• Wear protective clothing - gloves, heavy fabric, long sleeves, trousers sleeves and cuffs held closed by rubber bands, and don't forget to have a gauze veil around your head - hanging from a broad-brimmed hat and tucked into your collar.
• Oh, did I say - MOVE SLOWLY! You don't want to frighten the bees away!

What about humming birds? These wonderful little creatures are not good subjects for impatient young investigators because they are quite territorial and one will chase away others - and they might even try to chase you away. Although small, they have been known to attack large intruders by going for eyes. In brief: stick with the bees!

Let's suppose you have "prepared" a patch of several dozen identical flowers that had just moments before been in the process of being visited by many bees. You have SLOWLY moved about among them tearing all the petals off some, tearing away half the petals on others, making the petals shorter on still others, and altering the colors of still others. BUT you have left many untouched - they are your "controls."

See if you can now recruit a few friends to help you count visits. Give each of them a score card as shown to the right. It might help if each of you watches a different type of flower. Have them write atop their score card how many of the type of flower they are watching. As sophisticated scientists, you might want to count both "looks" and "visits", where a "look" can be recorded by a single stroke such as "/", and if the "look" becomes a "visit", you add the other stroke "\" to make an "X" or a "V", whichever is your preference. (If you click on the score card to the right, a new page will come up containing several blank score cards. Print the page and cut them out.)

• A "look" is when the bee hovers over the flower but doesn't land
• A "visit" is a touch-down

Treatment of Data

As soon as one of you reaches 100 "visits", everyone stops scoring.

1. Each person adds up their scores. Since all have scored for the same length of time and for the same number of flowers, you really don't need to divide your scores by the elapsed times or numbers as time and number will cancel out in the next calculation. (BUT if you scored for different periods of time or for different numbers of flowers, THEN you must do the division.)
2. Divide your score by the score of the unaltered flower, then multiply by 100 to make a percent. This will give you a number. Let's call this your flower-type's index of attraction "Ia". Of course, the person who was scoring the unaltered flowers has an Ia = 100%
3. By comparing the Ia's of the various flower-types, you should immediately see what most attracts bees - the number of petals, their color, their length.
4. If you have a camera, take a close-up shot of your patch of flowers. Some portraits of bees would be nice, too!

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