2246: Christmas Presents

Explain xkcd: It's 'cause you're dumb.
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Christmas Presents
"The parasitism might be mediated by a fungus!" exclaimed the biologist who was trying to ruin Christmas again.
Title text: "The parasitism might be mediated by a fungus!" exclaimed the biologist who was trying to ruin Christmas again.


This is the second Christmas comic in a row after 2245: Edible Arrangements. It is also the second comic in a row about presents, this one in particular calls them Christmas presents, and this comic was released on Christmas Day.

A Christmas tree cut down from the woods will typically be placed in a living-room soon after being cut down, and left standing there through the holiday season. On Christmas Eve or Christmas Day, or even earlier, presents are typically put beneath the tree under the lower branches. Once the tree is cut down, it will eventually start turning brown and/or losing its needles as it no longer receives any nutrients from its roots.[citation needed]

Based on this observation (on Christmas Day) some biologist (or Randall) concludes that the presents are a type of parasitic plant—that is, a plant that derives some or all of its nutritional requirement from another living plant. Since such a plant can use the sugars produced by the parasitized tree it does not necessarily have to perform photosynthesis by itself (although some parasitic plants such as mistletoe are photosynthetically active). If the parasitic plant is not doing photosynthesis it can live in the shade beneath a tree that it parasitizes as it has no need for light, and since it does not need chlorophyll either, it may not be green (e.g. Orobanche).

With presents often being wrapped in bright white and red colored paper, Randall concludes that this indicates a lack of chlorophyll, thus fitting with the idea of a parasitic plant. With the presents being in the shade of the tree and the tree's health suffering, the evidence can only lead to the conclusion that Christmas presents are parasitic plants.

In the title text a biologist says that "The parasitism might be mediated by a fungus!" While many parasitic plants attach themselves directly to the plant they are parasitizing (e.g. mistletoe, a parasitic plant which is often used to symbolize romance at Christmas) this is obviously not the case with the Christmas presents which are not growing out of the Christmas tree - which appears to rule out a parasitic relationship. However, the biologist has an answer for that: Some parasitic plants (such as snow flowers) do not attack the tree directly but instead form a connection to mycorhizal fungi. These fungi are receiving sugars from the trees and in turn provide it with mineral nutrients. By parasitizing these fungi, the snow flower can steal the sugars of the tree indirectly. One says that the fungus is mediating the parasitism.

Randall dismisses these words as coming from a biologist who is "trying to ruin Christmas again", which could have several meanings. It could be that the biologist really is just trying to ruin Christmas, and is trying to be more successful than in previous years by tying Christmas presents to fungus in people's minds. One might say that the biologist is not a "fun guy" for doing this. [citation needed]

It could instead be the case that the biologist is quite earnest in his belief that Christmas presents are harmful plant parasites and is attempting to spray the presents with a fungicide, which would probably be toxic and potentially contaminate not only the wrapping paper but also the presents inside their boxes.

Finally, it could be that the biologist is right, and Christmas presents are hosts to or otherwise associated with a parasitic fungus (and Randall's dismissal is a sign of his infection). There are some parasitic fungi that hijack the brains of host animals and alter their behavior. The most famous of these is probably Ophiocordyceps unilateralis, the so-called "zombie ant fungus", which causes its hosts to perch on a high plant to maximize the distance traveled by the fungus's spores. Ants have in turn developed strategies for detecting and removing infected members from the colony's territory. None of these fungi are known to infect humans, but they did inspire the zombie fungus in The Last of Us.


[A Christmas tree decorated with 16 balls and a star at the top with a high trunk with space for several presents beneath. About 13 presents with different patterns of paper and some with strings around. Three arrows with text at the blunt end points towards different areas. To the left one points to a present, beneath this one points to the area beneath the tree (the bottom of one present) and to the right one points to the tree.]
Bright white and red colors indicate a lack of Chlorophyll
Flourishing in the shade
Tree health suffering
[Caption beneath the panel:]
The evidence is clear: Christmas presents are parasitic plants.

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Just realized that the DgbrtBOT has not worked since December 13th. So great work for those that has created the pages since then. I did this one today. Seems like it takes some time after creation before the next comic button appears on the previous page...? Followed the "When the bot fails" section on the BOT page. --Kynde (talk) 20:43, 26 December 2019 (UTC)

Ah, that explains it. I saw the comic two hours before I finally gave up waiting on DgbrtBOT to do what it does (not thinking I'd have to do it instead). I even had time to jot down a nice explanation written up, including references to Myco-heterotrophy and Mycorrhizal network where it seemed relevent to mention them, but I like the one that's here now so... 23:09, 26 December 2019 (UTC)

That one comic used to confuse me greatly when instead of "parasitic", it had "parisitic" on its initial release. I wondered if it was a pun on Paris or something. Apparently just a glitch. https://web.archive.org/web/20191225165144/https://xkcd.com/2246/ Ck (talk) 23:19, 26 December 2019 (UTC)

This comic is a reference to mistletoe (a parasitic plant that is asociated with Christmas). That is where the "biologists ruining Christmas" come in; biologists are likely to point out that mistletoe is a parasite. 06:57, 28 December 2019 (UTC)

Upon reading the comic I thought that humans are mediating this particular parasitism (as the species that actually cut down trees and create presents), and biologist tries to insult those humans by suggesting that they are fungus. 18:03, 28 December 2019 (UTC)

Whoever put the pun in the explanation deserves a prize V (talk) 04:49, 29 December 2019 (UTC)

Could this be a more complex version of Toxoplasma Gondii that infects humans? https://www.smithsonianmag.com/science-nature/the-parasite-that-makes-a-rat-love-a-cat-86515093/