Some plants use smell to communicate. For instance, plants like cabbage can emit a volatile gas that warns their vegetable neighbors that danger is nearby–anything from caterpillars to garden shears.
Biologists experimented with plant sounds by placing powerful acoustic instruments on the roots of corn saplings which allowed them to hear the clicking sounds coming from them. When they placed the roots near a water source, they grew in that direction.
Other scientists have discovered that chili seeds can sense nearby plants even if they’re sealed in a box. They placed the seeds of chilli peppers into eight Petri dishes arranged in a circle around a et fennel plant. Fennel releases chemicals into the air and soil that slow other plants’ growth, and sure enough, the chili seeds exposed to the fennel germinated more slowly than other chili seeds that were not exposed to it, and when the fennel was sealed up in a box (even though it was still nearby, the chili seeds sprouted faster than usual.
The box should have blocked the fennel chemicals, so the seeds must have communicated in some other way–by sound?