How can that possibly be known. Look at the Venus flytrap. It is able to sense when a certain point on it is disturbed, and respond with an action. You can take any plant and set it four feet away from a window and it will naturally grow into the direction of light, therefor bettering it's own living conditions and chance of survival. Or simply the fact that many plants are known to very closely replicate the appearance of a certain insect in order to attract it, therefor adding to the chance of pollenation. I can name about forty different traits that plants show, that shows they do have instincts. Instincts show intelligence.