Welcome back to What a Plant Knows. In today's lecture, we're going to deal with something a little bit more controversial. What do plants remember? Now, I remember feeling nervous at the start of this class. What would it be like teaching for Coursera? I remember being hot under the lights, I remember the first sentence, even, from today's lecture. Now, we all have memories from earlier in life. Some of you even may have memories from very early in childhood. And quite often, our memories have to do with sensory information. We remember smells of things. We remember music, certain sounds. Now, as we've learned, plants live in a rich sensory environment. Now, plants obviously don't have memories the way we do. You know, they don't cower at the thought of a drought. They don't dream about the sunbeams of summer. They don't miss being encased inside the seedpod. They don't feel anxious about premature pollen release. you know unlike Grandma Willow in Walt Disney's Pocahontas, all trees don't remember the history of the people who sat under them or sat, or slept in their shade. But, as we've seen in earlier earlier classes, plants clearly have the ability to retain past events, to remember them, and to recall this information at a later period for integration into their developmental network. For example, we saw earlier in What a Plant Sees how tobacco plants know the color of the, the last color, of the light they've seen. Willow trees know if their neighbors have been attacked by caterpillars, and they remember this. So these examples and many more that we're going to talk about today illustrate a delayed response to a previous occurrence, which is a key component of memory. I want to give another example before we start going on into what are the mechanisms of plant memory. We talked about, when we were learning about plant responses to touch, about how tendrils can turn around the fence. A tendril is the extension coming off a stem, for example from a pea vine, that goes, grows out, and when it touches a fence, it starts curling. Now, again, one of the first people to study this was Darwin, and he showed that if you touch a tendril, and then remove that touch, it'll immediately start curling, and you can see this within several minutes. So there was an experiment that was done by Mark Jaffe in the mid 1970's. Mark Jaffe, Professor Mark Jaffe, the same scientist who coined the term thigmomorphogenesis. What he did was, he excised, he cut off a tendril from a pea plant, put it in a moist environment, and he found that this excised tendril could still respond to touch, even though it was no longer part of the complete plant. Then what he saw was that if he took this excised tendril and then put it in the dark, and touched it, it didn't start turning. But, if after it had been in the dark, he, while it was in the dark, he touched it, waited, say, 30 minutes, and then brought that tendril out into the light. Then it would immediately start turning, even though it had been touched several minutes, 30 minutes, even an hour earlier. It wasn't even, it wasn't needed complete lighting. As you could see, here in this picture from his original article, if he just gave it a small beam of light, just at the area where it has been touched, that's where it would immediately start bending. So, what we see here is another example of memory. Memory. We have three processes. We have the forming of the memory, which in the case of the tendril is encoding the information that it was touched. We have retaining the memory. It stores the touch information. And we have recalling of the memory, the retrieval of the touch information which is when it starts twirling. Human memory also uses these exact same three processes, the process of encoding, storage, and retrieval. Now, of course in human memory, we have many types of memories that we can define, for example short-term memory, which we can usually remember for a number of seconds, like in a phone number, you hear a phone number, you remember it for 10, 15 seconds Then after that you've forgotten it. We have long term memories where we,where we can recall instances that go back years, even decades of life. we have another type of memory which is called motor memory which musicians are very aware of. You know, if I ask a musician how does he play a guitar, move his fingers for a guitar or when you're playing piano, they can't really put it into words, but there's a memory of how to do the movements. We have another form of memory in our body which is called immune memory. When we get an innoculation, a shot, our body gets the information of a virus, it encodes the information that you've been exposed to the virus, and then it retrieves and responds to that information if you're exposed in the future. This is immune memory. This is interesting because this also illustrates that not all memory has to be neuron or brain based. Immune memory is obviously based in our immune system, our white blood cells, and not in our brain, but it still has the exact three functions, of encoding the memory, storage of the memory, and retrieval at a later date.