So is it too much anthropomorphizing to say that the tomato and the dodder, the tomato and the cuscuta are communicating with each other? Or even more out in left field, can we ask what plants talk about? I know that this is controversial, and especially the language I'm using, but I want to use it to help make a point right now. because there was an observation in the late 1970s, early 1980s, primarily by two scientists at the University of Washington, David Rhodes and Gordon Orians. And what they noticed is the following. If you look at trees that have been attacked by caterpillars the trees that were growing next to them, and this is out in the forest were often resistant to the caterpillars. And this was even though there would be no physical connection between the trees. The branches wouldn't be touching, the roots weren't touching. So how was it that here on the one hand you have a tree that's attacked by caterpillars, on the other hand you have a tree that's resistant? Not only was it resistant, they found out the reason it was resistant to the caterpillars is because those leaves were making chemicals, which are called phenolic compounds, or tannin compounds. Which are actually poisonous to the bugs. So how could this be happening? Their hypothesis was that the attack trees were releasing some type of airborne signal. Which was then signalling to the neighbor, watch out, start making these chemicals to protect yourself. This hypothesis was picked up and studied by two scientist at Dartmouth College, Ian Baldwin, who is then a graduate student, and his mentor Jack Schultz. And they decided to test this hypothesis in the laboratory. And their results were so ground breaking that they were published in the very prestigious Journal of Science in an article that was called Rapid Changes in Tree Leaf Chemistry Induced by Damage, Evidence for Communication Between Plants. So, here is the experiment that they did. They studied both poplar and sugar maple seedlings. Seedlings of trees are about a foot tall so there not very small. What they did is they built airtight plexiglass cages. And in these cages they put about 15 of the seedlings. They used two different cages for two different conditions. In the first cage they put 15 seedlings but to two of the seedlings they ripped their leaves. So within this cage, you have two seedlings with leaves that have been ripped, and the rest have been untreated. In the second cage, you had the same number of tree seedlings, but their leaves were not ripped at all, they were just left there as a control. So again, so we have three different types of seedlings in one cage. Two trees with ripped leaves, the rest without ripped leaves. And in the other cage, nothing had been done to the seedlings. After two days, they came back, then measured the chemicals in the leaves. Now when they measured the chemicals in the leaves from the trees that had had their own leaves ripped, they found that these leaves made those same anti-bug chemicals. It was as if the ripping of the leaf was the same effect as having a bug come and eat the leaf. But not only did those same seedlings that had had their leaves ripped make those chemicals, but the other trees in those same boxes, the same trees whose leaf had remained intact also made those chemicals. So what Baldwin and Schultz proposed was that the damaged leaves whether by tearing as in their experiment, or by the caterpillars foraging on them as in the earlier experiment from the University of Washington, cause the leaves to release a volatile signal. A gas up into the air which was then picked up by the neighboring leaves. And is this gas which is telling them to make the anti bug chemicals. And then these trees which would then start making the chemicals would be protected against an imminent insect attack. So does this actually mean that the trees talk to each other? Would that be our interpretation of these results? Again what we're seeing out in nature was from Orians and Rhodes' experiment. That the tree that was infected by the caterpillar releases a gas into the air. Its neighbor then absorbs this gas. Starts making the chemicals and becomes resistant to the caterpillars. Now this result was incredibly controversial. On the one hand, the popular press loved it. Some of the, many newspapers around the world started publishing articles. One saying for example, scientists turn new leaf, find trees can talk. Another newspaper headline said, Trees Talk, Respond To Each Other. Even the respected New York Times had an article that said, when trees talk. On the other hand, scientists were much, much more skeptical about the result. With many thinking that the results were completely over-interpreted. So much so, that in 1985, scientists from the University of York, even published an article where they said, we believe that much of the evidence in this general field is unsatisfactory. I need to say it takes quite a lot for a scientist to come out publicly. And actually published a paper against the results of someone else. But here I want to take a second to talk about science as a self correcting process. There can be results that people don't agree with or there can be results that people do agree with. What's wonderful about the process of science is that, in the long run, the good science, the science that's done with proper controls, in the end tends to become accepted. Whereas pseudoscience, science that's done with improper controls, is often relegated to what I call the wastebasket of scientific history. We saw that in the first lecture when I talked for a second about Barbara McClintock and her jumping genes. A process which most scientists didn't accept in the beginning but she later got the Nobel Prize. So Baldwin's results have since been repeated in numerous laboratories using many different types of plants. Volatile signaling between plants is now an accepted paradigm.