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You can go to linode.com/scishow to learn more and get a $100 60-day credit  on a new Linode account. [ INTRO ] If you look at the individuals of one  species, often they’re pretty similar looking. An elephant is going to look very  similar to a fellow elephant, at least in terms of its general  arrangement of limbs and stuff.

But individual trees can often  have one or more growth features that make them quite unique from their  neighbors, especially as they get older. Maybe it’s a large knotted  hole where a branch used to be, a big gnarled burl bulging out from the side, or even a completely hollowed out trunk  that makes a particular tree noteworthy. And these unique features didn’t just  grow as part of these trees by chance.

They’re actually the scars of  past battles against infections that raged on at the cellular  level, sometimes for years on end. When a tree gets wounded, say from a fire  or an insect borrowing through the bark, it’s not just that immediate  damage the tree has to worry about. Much like our own scrapes and cuts, there’s also a risk of an infection getting  into the wound and causing some serious issues.

The pathogens, or infectious agents, that  you most often see with tree wood are fungi. And these fungi can make their way  into a tree through a crack or wound, slowly decaying it from the inside out. Luckily for the tree, it isn’t  helpless against these infections.

Trees have developed incredibly  successful protective measures   against the fungi that try to take them down. Given that trees in all different environments  are going to be encountering fungal foes, it makes sense that both  coniferous and deciduous trees from around the world use these types of defenses. That’s because plants have evolved  a lot of built-in defenses, given that they can’t exactly  run away from their enemies.

Whether it’s a fir, spruce, pine,  beech, oak, maple, or a plum tree, you can bet it’s well prepared  to face fungal invaders. In response to an injury, the tree can basically slam shut  containment gates all around the wound. The tissues surrounding the  compromised area become calloused, growing a thicker and denser woody boundary  by reinforcing the cell walls in that area.

This process also produces a bunch of  new cells to form an additional boundary between the wound and surrounding tissues. Those cells in turn grow tyloses, outgrowths that essentially dam up the tissues. And these tyloses are so  tough against fungal decay, they’re often left intact long after  the rest of the tree has rotted away -- if it loses the battle, that is.

This new growth compartmentalizes  the infected area and prevents the fungus from getting  through the vulnerable xylem cells. That’s the tissue that transports water – and could otherwise give the pathogen  a free ride throughout the tree. By sacrificing the tissue that’s  already in contact with the fungus and cutting it off from  healthy surrounding tissue, the tree can pull off some  significant damage control.

But the defensive measures don’t end there. The cells that form this protective  layer also produce fungicidal agents that help keep unwanted invaders in check. Along with the physical barrier,  injured trees also produce significantly more phenolic compounds.

These chemical compounds are  found in most plant tissues, and trees start pumping out even  higher concentrations of them in woody tissues that have  recently become wounded. Phenolic compounds are very diverse  in what they can do for plants, but in the case of those that  get released after injury, it appears their purpose is to  directly fight off the offending fungi. While the full extent of what is  happening isn’t yet understood, the compounds seem to be directly  inhibiting the growth of the fungus, stopping it in its tracks.

And that’s not all. The tree releases  a whole tide of chemicals and proteins, whose function we’re still unraveling. Combine these defensive measures, and you have a fungus that’s stuck  in its tracks with nowhere to go.

Even though the tree-versus-fungus battle  is happening at the cellular level, the results manifest  themselves in a number of ways. Trees may develop thick growths and  scars along their trunks and branches, or have big knotted burls bulging out  the sides of their branches or trunks. Some trees, like European beech, are prone to discoloration as a result  of their battles against infections.

Even though the trees remain relatively healthy, the resulting aesthetic effects are often  frowned upon in the forestry industry because it makes the wood less valuable. These battles can even result in a  nearly completely hollow tree trunk, as some fungi species specialize in decaying  heartwood, the inner core of a tree. But as long as the growth tissues of the  tree are protected from the fungal infection, the tree can continue to thrive  even if its core has rotted away.

Because heartwood is actually dead – those interior cells die off as part of  the natural, healthy growth of the tree. But of course, no defense is perfect. Some fungi can degrade the tree’s barriers to   keep eating away at the wood,  eventually killing the tree.

And producing these physiological and  chemical defenses is costly to the plant. That’s why they concentrate their  efforts only on wound sites, instead of being distributed  throughout the tree at all times. It’s just not worth the energy  to be in defense mode 24-7.

So the tree doesn’t always win  this battle, and even if it does, it may face some pretty dramatic  physical consequences as a result. That said, they certainly are very effective  at limiting the damage done by fungal invaders. If they weren’t, trees would probably  be wiped off the planet pretty handily.

So the next time you see a gnarled, knobby tree, commend it on its perseverance through  some intense internal conflict.   If you’re conflicted about which  cloud computing service to use,   you can go to Linode’s website where they show you  side-by-side comparisons of different providers.   Linode offers cloud computing  that meets you where you are.   Just like in a SciShow  video, the people at Linode   don’t assume that you came to them already  knowing everything about a given topic.   That’s why Linode offers videos,  blog articles, customer support,   and online tools to help you  learn how to set up your own   cloud services like a website or personal VPN.   The list of cloud computing services ranges  from added storage to customized apps.   And Linode won’t force you to pay  for services you’re not using.   They have simple plans with capped  pricing to keep your bills low.   To figure out how much the specific  services you’re interested in using cost,   you can play around with their price estimator  tool for free before committing to anything.   And once you decide to take the plunge,

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