Research assistants with the Darwin Correspondence Project joined the teaching team for a new Freshman Seminar at Harvard College called “Getting to Know Darwin.” The class was composed of first year undergraduates and was taught by Ned Friedman, Director of the Arnold Arboretum at Harvard University and Professor in the Department of Organismic and Evolutionary Biology. Here is a link to a feature about the course.
To learn about Darwin’s work on climbing plants, the class took a field trip to the Arnold Arboretum. At the Arboretum, students were able to observe the various methods of climbing used by plants. Climbing has a few key evolutionary benefits for plants. Firstly, it saves plants energy: rather than developing their own support systems, climbing plants rely upon their surroundings for support. This saved energy enables climbing plants to devote more energy to leaf development and rapid growth. Climbing plants are also able to grow above other plants, thereby enabling them to reach sunlight in crowded areas.
After observing the plants at the Arnold Arboretum, the class conducted a simple experiment to observe the curling action of cucurbitaceous tendrils. The curling action in these tendrils is significant; it enables the plant to latch onto supports and climb ever higher. In the experiment, the students found that rubbing a textured coffee stick along a tendril causes the tendril to curl within seconds. Through this experiment the students, just like Asa Gray and Charles Darwin, were able to study the sensitivity and rapid movements of tendrils. This experiment can be easily replicated – all you need is a cucurbitaceous plant and a coffee stick! See if you can replicate Darwin’s findings on the actions of tendrils, as described in the following excerpt from an 1863 letter he wrote to the English botanist J.D. Hooker:
This may be common phenomenon for what I know; but it confounded me quite when I began to observe the irritability of the tendrils.— I do not say it is final cause, but the result is pretty for the plant every 11⁄2 or 2 hours sweeps a circle, (according to length of bending shoot & length of tendril) of from 1 foot to 20 inches in diameter, & immediately that the tendril touches any object its sensitiveness causes it immediately to seize it.
For added drama, create a time lapsed video of the cucurbitaceous tendril as it twirls towards the coffee stick. A sample video is available here.