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第1段
1 .Listen to part of a lecture in a biology class,
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2 .when you see a mushroom growing in the forest, you\'re actually looking at just a small part of a much larger fungus。
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3 .underneath the mushroom, underground。
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4 .you\'ll find the rest of the fungus a network of thread like structures.
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5 .These individual thread like structures are called hyphae。
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6 .and the network of these hyphae is called a mycelium.
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7 .In some cases, my Celia can be huge structures weighing hundreds of tons.
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8 .We\'ll go into more detail about them later this week, but for now, you have the basic idea.
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9 .Okay, back to the mushroom on the surface.
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10 .The mushroom is the fruiting body of the fungus.
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11 .Its primary function is to produce and nourish spores.
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12 .Spores are to a fungus what seeds are to a plant.
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13 .They\'re the reproductive bodies.
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14 .Spores are tiny, most of them consisting of just a single cell.
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15 .Now, if you knock a mushroom over and look at the under surface of the cap.
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16 .it\'ll look something like this.
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17 .The flat, thin structures that you see radiating out from the center are called gills.
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18 .and it\'s deep inside these gills that the spores are produced.
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19 .Once the spores mature, they\'re released.
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20 .and they fall down through the spaces between the gills and out into the air below the cap.
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21 .where they can be carried away by the wind.
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22 .hopefully to some location that\'ll give them at least some chance of surviving, of developing into a mature fungus.
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23 .Now, when the mushrooms in its normal upright position, the gills have a nearly perfect vertical orientation.
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24 .Why does that matter?
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25 .Well, when the spores are released, gravity pulls them straight down.
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26 .So if the gills didn\'t have this orientation.
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27 .the spores would be forever bumping into them as they fell.
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28 .And these spores are very sticky.
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29 .so if they come into contact with the gills, they\'re going to stick to them.
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30 .and they\'re never going to go anywhere.
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31 .Okay, so what do you think of the mushroom strategy, if you will, for dispersing its spores?
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32 .Jennifer. It seems like a good system. You\'ve got a stock raising the cap above ground so the wind can get under it and carry the spores away.
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33 .And you\'ve got these, like, tiny little spores that are really light, so it doesn\'t take a lot of wind to carry them.
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34 .Yes, the system looks well designed.
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35 .but despite this seemingly efficient design, mushrooms have to produce millions, even billions, of spores.
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36 .Why so many?
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37 .Well, it turns out that many spores are not carried very far.
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38 .they land within a meter or so of the mushroom.
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39 .but that\'s an area where, as we said, there\'s already a mycelium established underground.
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40 .So that\'s not a suitable area for a new fungus to grow.
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41 .and some of the spores get carried farther, but many of those land in inhospitable habitats. Oh, okay.
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42 .but fungi that do not depend on the wind.
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43 .that disperse their spores in other ways, can have a much higher success rate.
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44 .For example, some of you may be familiar with truffles.
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45 .Some species of truffles are edible and considered delicacies.
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46 .like the mushrooms we just discussed.
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47 .A truffle is the fruiting body of certain species of fungi.
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48 .Unlike mushrooms, however, truffles grow underground.
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49 .and the primary mechanism they use to disperse their spores is very different.
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50 .You see, it\'s not just humans that like truffles.
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51 .As a truffle spores mature, the truffle develops an aroma that attracts many kinds of animals.
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52 .In fact, Europeans have for centuries been using pigs to locate and extract truffles.
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53 .Recently, they\'ve begun using dogs instead of pigs. As dogs are less intent on eating the truffles they find.
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54 .Also, most people would rather spend their time with dogs than with pigs.
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55 .Anyway, when a wild animal, say, a deer finds some truffles and eats them.
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56 .The spores remain intact in its digestive system.
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57 .The deer then walks on for a while, and at some point, it\'ll excrete waste from its digestive system, and the truffle spores will get deposited in that new location.
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58 .Yes, Eric.
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59 .So how is that more efficient than the way mushrooms disperse their spores?
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60 .Well, the deer carry the spores a nice distance away from the original truffle right.
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61 .to habitats that are conducive to the growth of truffles, right?
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62 .Whereas the wind might not pick up the spores at all, or might deposit them in like the middle of a Lake or something.
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