[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:07.45,0:00:10.07,Default,,0000,0000,0000,,If you were a jackrabbit hopping through \Nthe desert,
Dialogue: 0,0:00:10.07,0:00:15.79,Default,,0000,0000,0000,,you'd be glad to stumble, well, maybe not\Nstumble, across a cactus. The succulent
Dialogue: 0,0:00:15.79,0:00:20.46,Default,,0000,0000,0000,,flesh of these plants is a water source\Nfor many desert animals. Native to the
Dialogue: 0,0:00:20.46,0:00:22.13,Default,,0000,0000,0000,,Americas and known for
Dialogue: 0,0:00:22.13,0:00:27.32,Default,,0000,0000,0000,,their spines and succulent stems, cacti \Nof all shapes and sizes have evolved to
Dialogue: 0,0:00:27.32,0:00:32.90,Default,,0000,0000,0000,,not just survive, but thrive in some of \Nthe harshest desert climates on earth.
Dialogue: 0,0:00:33.45,0:00:39.63,Default,,0000,0000,0000,,So, how do they do it? A cactus's spines\Nare key to its survival, but not for the
Dialogue: 0,0:00:39.63,0:00:44.62,Default,,0000,0000,0000,,reason you might think. Take a look at\Nthe Prickly Pear. Its spines are highly
Dialogue: 0,0:00:44.62,0:00:50.09,Default,,0000,0000,0000,,modified leaves. A normal leaf's large \Nsurface area would be ill-suited to the
Dialogue: 0,0:00:50.09,0:00:54.32,Default,,0000,0000,0000,,desert, transpiring massive amounts of \Nwater under the baking sun.
Dialogue: 0,0:00:54.32,0:00:55.32,Default,,0000,0000,0000,,The dramatically
Dialogue: 0,0:00:55.32,0:01:01.25,Default,,0000,0000,0000,,reduced surface area of the spines limits\Nwater loss. They also shade the cactus,
Dialogue: 0,0:01:01.25,0:01:06.30,Default,,0000,0000,0000,,and reflect the sun's rays, reducing the \Nthe plant's core temperature during the
Dialogue: 0,0:01:06.30,0:01:11.53,Default,,0000,0000,0000,,heat of the day. Then, at night, when air \Ntemperatures plummet, the spines act as
Dialogue: 0,0:01:11.53,0:01:16.10,Default,,0000,0000,0000,,an insulating layer, keeping the cactus\Nfrom cooling down too much. These
Dialogue: 0,0:01:16.10,0:01:20.86,Default,,0000,0000,0000,,functions are just as important, if not\Nmore, than defending against predators.
Dialogue: 0,0:01:21.92,0:01:28.06,Default,,0000,0000,0000,,From Cuba to Mexico, and as far south as \NBrazil and Peru, Melon Cacti grow on
Dialogue: 0,0:01:28.06,0:01:33.58,Default,,0000,0000,0000,,limestone soils in seasonally dry tropical\Nforests, where they're constantly exposed
Dialogue: 0,0:01:33.58,0:01:39.57,Default,,0000,0000,0000,,to the beating sun. They rely on another \Nadaptation common to cacti: a thick skin,
Dialogue: 0,0:01:39.57,0:01:44.61,Default,,0000,0000,0000,,which is coated in a waxy substance called\Na cuticle that limits water loss.
Dialogue: 0,0:01:44.90,0:01:50.53,Default,,0000,0000,0000,,Meanwhile, the Stomata, tiny holes that\Nallow the exchange of gases that enable
Dialogue: 0,0:01:50.54,0:01:56.32,Default,,0000,0000,0000,,photosynthesis, remain firmly closed until\Nnight, when they open. The lower
Dialogue: 0,0:01:56.32,0:02:01.05,Default,,0000,0000,0000,,temperatures at night mean the cactus \Nloses less water from the stem when
Dialogue: 0,0:02:01.05,0:02:06.33,Default,,0000,0000,0000,,Stomata open. The bulk of the plant acts\Nas a large barrel of water, storing it
Dialogue: 0,0:02:06.33,0:02:11.19,Default,,0000,0000,0000,,for times of need. But to survive the\Ndesert, the cactus can't just limit water
Dialogue: 0,0:02:11.19,0:02:15.62,Default,,0000,0000,0000,,loss. It has to be prepared to take \Nfull advantage of the rare situations
Dialogue: 0,0:02:15.62,0:02:20.97,Default,,0000,0000,0000,,where water is readily available. In North\NAmerica's Sonoran Desert, the towering
Dialogue: 0,0:02:20.97,0:02:27.09,Default,,0000,0000,0000,,Saguaro Cactus can grow up to twenty \Nmeters tall and live for up to 200 years.
Dialogue: 0,0:02:28.39,0:02:32.45,Default,,0000,0000,0000,,Woody tissue, like the kind found in \Ntree trunks, gives the Saguaro its
Dialogue: 0,0:02:32.45,0:02:38.05,Default,,0000,0000,0000,,height, but the Saguaro survives with way\Nless water than most trees. Most of its
Dialogue: 0,0:02:38.05,0:02:43.80,Default,,0000,0000,0000,,roots are only a few inches deep, just\Nbelow the soil's surface. The spread out
Dialogue: 0,0:02:43.80,0:02:49.74,Default,,0000,0000,0000,,laterally for meters, and hold the plant\Nin place. Even its single deepest root,
Dialogue: 0,0:02:49.74,0:02:56.12,Default,,0000,0000,0000,,the tap root, extends less than one meter\Ninto the ground. After a rain, the lateral
Dialogue: 0,0:02:56.12,0:03:01.42,Default,,0000,0000,0000,,roots respond in real time, rapidly \Ngrowing and spreading. They produce
Dialogue: 0,0:03:01.42,0:03:06.45,Default,,0000,0000,0000,,ephemeral rain roots that quickly take up\Nthe available water. The water is then
Dialogue: 0,0:03:06.45,0:03:12.14,Default,,0000,0000,0000,,pulled up into the plant body and stored\Nin cells that contain Mucilage, a gluey
Dialogue: 0,0:03:12.14,0:03:17.07,Default,,0000,0000,0000,,substance that clings to water molecules\Nand stops them from evaporating if the
Dialogue: 0,0:03:17.07,0:03:22.46,Default,,0000,0000,0000,,plant's tissue is ever damaged and \Nexposed. As the soil dries after the rain,
Dialogue: 0,0:03:22.46,0:03:27.68,Default,,0000,0000,0000,,the small rain roots also begin to dry\Nand wither away, and the cactus awaits
Dialogue: 0,0:03:27.68,0:03:31.95,Default,,0000,0000,0000,,the next time it can take advantage of a\Nshower. Taken together, these features
Dialogue: 0,0:03:31.95,0:03:36.65,Default,,0000,0000,0000,,make cacti well-equipped to survive their\Nenvironments, from the driest desert to...
Dialogue: 0,0:03:37.12,0:03:42.70,Default,,0000,0000,0000,,a tropical rain forest? The Mistletoe \NCactus can live on the branches of trees
Dialogue: 0,0:03:42.70,0:03:47.76,Default,,0000,0000,0000,,in the rain forest. Though there's lots of\Nwater around, not much of it reaches the
Dialogue: 0,0:03:47.76,0:03:52.100,Default,,0000,0000,0000,,cactus here, and there's nowhere for its\Nroots to go. So, even here, the cactus
Dialogue: 0,0:03:52.100,0:03:53.76,Default,,0000,0000,0000,,survives
Dialogue: 0,0:03:53.76,0:04:00.41,Default,,0000,0000,0000,,using adaptations that long ago helped\Nits ancestors survive the desert. Other
Dialogue: 0,0:04:00.41,0:04:06.06,Default,,0000,0000,0000,,plant adaptations more closely resemble \Nbooby traps, from Bedbug Harpoons to
Dialogue: 0,0:04:06.06,0:04:10.95,Default,,0000,0000,0000,,Fly Swatters. Check out some of the \Namazing ways plants defend themselves with
Dialogue: 0,0:04:10.95,0:04:12.33,Default,,0000,0000,0000,,this video.
Dialogue: 0,0:04:12.33,0:04:20.00,Default,,0000,0000,0000,,♪ (Music) ♪