A benefit to not having a brain is that when a plant is eaten, it doesn't die. It can resprout and stay alive.
Plants can also remember things, such as a stimuli being repetitively tested, and change their response over time.
I can't believe that plants can apparently hear - if you play caterpillar munching sounds to a plant, it can start increasing its defensive compounds without being eaten at all! (Disclaimer: I was not able to find the scientific study in a Web of Science and Google search, but Pollan said it was done by Heidi Appel, a chemical ecologist at the University of Missouri).
I didn't read through Pollan's article in the New Yorker yet, but if you prefer to read, and have time to read 11 pages, then here it is. I believe it has more information on scientists and their studies if you want to find some of these sources on your own (and if you do, please sha