Plants have any number of methods to communicate both internally and externally in order to keep themselves informed and respond to their environment and developmental needs. They use this vast array of capacities to negotiate their way toward maturity and reproduction among other things. As it turns out, plants have a rich social life. They are for instance able to forge relationships with various benefactors in the plant and animal kingdoms and coordinate their effort, including the recruitment of other creatures, to ward off antagonists. They sense, and think without the means of a brain as we understand brains, yet they have the capacity to perceive and respond on remarkable levels which we are only beginning to understand. Here is a documentary on some of the recently discovered attributes of plants.
The Wisdom Of Life 