Think of ways that plants can communicate with each other: First, there's chemical signalling, where a plant releases chemicals into the air or soil which are then sensed by nearby plants.
There's touch - plants can respond to physical sensation either by a competing or parasitic plant growing nearby or an herbivore trying to eat it.
Then there's light - though this is a bit indirect. Plants can sense the level of light and indirectly gauge proximity of neighboring plants - for example, it can figure out that it's in a crowded neighborhood by perceiving the levels of certain wavelengths of light.
All those methods of communications are known. So how can you explain these results by Monica Gagliano at the University of Western Australia in Crawley and colleagues?
First, some background: sweet fennel (Foeniculum vulgare) sends out chemicals that can retard the growth of chilli peppers (Capsicum annuum) plants. So, chilli peppers grown near a sweet fennel would germinate more slowly than those grown by itself. Got that?
Here's the fun part: researchers placed a sweet fennel plant in a box and then surround it with chilli pepper seeds. In the first experiment, the sweet fennel is in an open box (so the chemical signals can reach the chilli peppers). In the second experiment, there's no sweet fennel in the box. And in the third, the sweet fennel is in a sealed box.
So, what do you think will happen?
Here's what she found:
1) The chilli peppers grown in the first experiment will germinate more
slowly than the second. Just as expected.
2) The chilli peppers grown in the third experiment - where the seeds are nearby the sweet fennel plant, but no chemical or light signal can reach them, actually grow faster than the chilli peppers grown next to an empty box.
So how in the world did the chilli peppers know that there's a sweet fennel in that box?