At the beginning of the lecture, when I talked about specific mechanosensitive organs in humans, there was one that I ignored. Those are the mechanosensitive hairs in our ears, which respond to vibrations. If plants respond to touch, if they know when there's a mechanosensitive stimulation of their leaves, or their stems or their roots, is it possible that plants also respond to vibration just like our ears do? In other words, do plants hear? Before we continue exploring if plants hear, I want to ask you a question. Which music do you think plants prefer? Heavy metal, classic rock, maybe, maybe Muzak like in elevators, maybe Indian sitar music, or how about classical music? Take a second, think about what music you think plants prefer, and let us know here on the screen. It's probably not too surprising to know that you're not alone in wondering if plants have musical tastes. I'll ask you, who was one of the first people to study this, to do experiments, and I hope by now you're also not surprised to know that it was none other than Charles Darwin, who, as we've seen, has also studied other plant senses. In one of his more bizarre experiments, Darwin monitored the effects of his own bassoon playing. Yes, Darwin played the bassoon, as did his son, on plant growth by seeing if he could get his bassoon music to cause the Mimosa leaves to close, just like touching the Mimosa leaves causes them to close. Well, the result was that he couldn't, and in his own autobiography, Darwin described this experiment, in his own words, as a fool's experiment. So, while there are hundreds of articles that support plant responses to light, to smell, to touch, there's hardly any credible research that show plants responds to sounds. Actually, there's an inverse correlation to the dearth of research to plant responses to sounds and the popular belief that plants prefer one type of music over another. Actually, I'm sure that many of you were surprised to learn that plants can smell each other, but at the same time you're convinced that plants, or you've heard that plants, have musical tastes. Now the reason that many of you have heard this is because the popular press has shown articles, has shown research that's seemingly showing plants responding to sounds and even to music. One of these was published in the early 1970s in a lovely book called The Sound of Musical Plants. Now, this book gives a lovely image of a nun singing to her plants maybe up in the Swiss Alps in The Sound of Music, and her plants responding. The results of this book were actually picked up in another book, which many of you have heard of called The Secret Life of Plants. They talked about these results of these plants responding to music. Let's see exactly what these experiments were. These were experiments that were carried out in the 1960s by a woman named Dorothy Retallack. Mrs. Retallack was an undergraduate student, she actually went back to college in midlife to be a music student. She herself was a musician and she had a biology requirement, so as part of her biology requirement, she decided to see if plants respond differently to different types of music. Now you have to put yourselves into the mid year of the 1960s. This was, the culture revolution's going on in the United States, rock music, counter culture. Mrs. Retallack was not a big rock and roll fan, and one of the reasons she did this experiment was to see if rock and roll had a negative effect on plants, and then she could also say that it had a negative effect on the nation's youth. What she saw, actually, and here's a picture from her research, is that, when her plants were exposed to Jimi Hendrix or to Led Zeppelin, some of them wilted, whereas if she played for them Robby Shankar's Indian sitar music, they thrived. So, coming from this, and especially someone who grew up during this time, it's a little bit disconcerting to think that maybe rock and roll can cause art development to be inhibited. Well, but fortunate for me and hordes of other Led Zeppelin fans out there, Retallack's studies were fraught with scientific shortcomings. I think it's very important to go through, what are the problems in her experiments, to understand what solid research is versus what is pseudoscience. First of all, each of her experiments included only a small number of plants, actually less than five, and her number of replicates were so small that it was not sufficient for any statistical analysis. On top of that, her experimental design was very poor, some of the studies were carried out in the lab, some of them were carried out in her neighbor's house and her friend's house. Parameters that are very important, such as soil moisture, were determined by touching the soil with her finger to determine if it was moist or not. Also, if you read her book, you'll see that there's a number of citations, which makes you think that it's scientifically valid, except most of these citations are not from biologists. They were from experts in theology and experts in music, but there are very few citations which have any scientific credentials whatsoever. Most importantly, none of her research has been replicated in any lab anywhere in the world. This is actually the key point. Research is self-correcting, if we publish something that's not originally accepted, if it would be repeated in many labs, then the scientific community will start accepting it. These experiments, music and plants are so easy to replicate that, if there was any true science going on here, believe me, many labs in the world would be following up on this research. Actually, one of the other problems in scientific research is that you can't publish negative results. For example, if someone's lab had studied the effect of music on plants and found that there was no effect, this isn't something that you really publish very often. Indeed though, careful examination, and as scientists we have to really examine things closely. Of the scientific literature reveals that there are certain results, negative results, that have been peppered throughout significant scientific papers that completely debunk the idea that plants have musical taste. For example, earlier in today's lecture, we talked about Janet Braam's experiments and the touch genes. In this paper on the touch genes, which is a seminal paper, very important paper, published in a very prestigious journal, she also checked to see that the touch genes could be induced by loud music, which for her came from Talking Heads. It's actually very interesting to think how this lets us know what the musical tastes of the authors were. And alas, the touch genes could not be induced by exposure to the music of the Talking Heads. I want to just talk about just one other experiment that was published in a textbook, the textbook called Physiology and Behaviour of Plants by Peter Scott. In this textbook, he reports a series of experiments that were set up to test whether corn is influenced by music. Again, in this case, it's interesting which music he chose. He used Mozart's Symphony Concert Ten and Meatloaf's Bat Out of Hell. So, let's listen for a second, and what do you think will happen? So, here are the experimental results. What he was checking was the effect of music or silence on germination of corn, so here's the first result. In this graph, we see the amount of germination over time, 2, 3, and 4 days. The green bar shows the amount of germination in the control plants. These are the plants that were not exposed to music, that were kept in silence. The blue bars show the amount of germination when the corn was exposed to Meatloaf, and the red bars show the about of germination when the seedlings were exposed to Mozart. As I think it's clearly shown, both at 48 and 72 hours, the germination of the corn was enhanced when they were exposed to music, but we also see that there was no difference between hard rock and classical music. This could actually support those who claim that music affects plants, but it also really hurt people like Dorothy Retallack, who thought that rock and roll is quantitatively much worse than classical music. But, now let's continue to see how they continued the experiment, and this is where the importance of proper experimental controls comes in. The experiment was continued, but this time between the speaker and the seedlings the scientist put a small fan, which would blow away any of the heat that was coming off the speaker. Now let's look at the results here, where we can see now within the presence of the fan, there's no difference between the green bars, which are the seedlings kept in silence, the seeds kept in silence, the blue bars, which was MeatLoaf, and the red bars, which was Mozart. In other words, the results that were originally shown that music increased the germination is likely a result of the heat coming from the speaker and has absolutely nothing to do with the music. The heat was the deciding factor, not Mozart nor Meatloaf's music, in contrast to Ian Baldwin's initial studies on plant communication And volatile chemicals, which I talked about in the third lecture. In other words, the experiments where he showed that plants smell each other. Remember, these experiments were originally met with resistance by the mainstream scientific community, but they were subsequently validated in many labs and have now become a paradigm. Retallack's musical plants have not been validated, and these results have been relegated to the garbage bin of science. If you're interested in reading about some more quite zany plant-music experiments, you could read in our textbook what a plant knows on the following pages.