A tomato plant, perhaps one of the varieties featured in the below research. Source: Wikipedia. License: cc-by-2.0

LiveScience.com reports on a new, yet-to-be-peer-reviewed study that claims some plants, when stressed, emit sounds in the ultrasound frequency. The study is available at https://www.livescience.com/plants-squeal-when-stressed.html.

This seems rather unbelievable because to emit sound you need to have some kind of equipment that can compress air in a specific manner and it’s unlikely that plants would have capabilities for such a specific act. It must be the case that the plants aren’t emitting intentionally so much as it being an epiphenomenon, ie, a consequence of something else—perhaps, being stressed. For example, herbivorous animals defecate when being chased by predators. This isn’t because they expect the stench to drive away the predator, rather, when it’s a question of life or death, the herbivore’s digestive system shuts down—with shitty consequences.

Sure enough, the LiveScience article’s report is along the same lines. They say:

In plants stressed by drought, air bubbles formed, popped and triggered vibrations within the tissue that normally carries water up the plants’ stems.

In other words, the plants had gas.