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What are the bumps on this tomato stem? They are way off the ground so I doubt they are air roots.

What are they, what function do they have and why do they form? enter image description hereenter image description here

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Those bumps are aerial surface hairs, a type of trichome. They are epidermal outgrowths. Therefore it's vines are of pubescent type.

In addition to facilitating better exchange of gases, it also facilitate the vining process, turning into roots wherever the plant is in contact with the ground and moisture, especially if the vine's connection to its original root has been damaged or severed.


Sources:

1:https://en.m.wikipedia.org/wiki/Trichome#/search

2:https://en.m.wikipedia.org/wiki/Tomato

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  • $\begingroup$ I'm very skeptical of the claim that these trichomes facilitate gas exchange or vining, or become roots. The long spiky trichomes are almost certainly for defense. The shorter fuzzy trichomes may serve to increase the air boundary layer, thereby decreasing moisture loss, but one can see that many of these shorter ones are gland-tipped, so they are probably also involved in defense. Trichomes come from only the outer epidermis cells, so they themselves wouldn't "turn into roots", though they do come from a similar developmental process as root hairs, which may explain the confusion. $\endgroup$ Commented Mar 9, 2023 at 17:14

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