Commenting on my last post about plant behaviour, Jim mentioned a paper by Marian Smith on plant responses to being touched or shaken. Unfortunately I couldn't get the link to work, but I did a Google Scholar search on the name & topic & got this: Plant growth responses to touch - literally a 'hands-on' exercise! It's in JSTOR so should be accessible for teachers & students interested in this paper, published in The American Biology Teacher (the link's to the JSTOR backfiles of this journal).
Most people would be familiar with the rapid responses to touch shown by venus flytraps & mimosa plants (one being what you could describe as a 'predatory' response, & the other quite possibly an adaptive response that reduces damage from herbivory - fascinating stuff & I must write something more about it). But that would be it. However, it seems that most plants have a distinct, measurable growth-response to mechanical stimulation (Smith, 1991). This response tends to be a reduction in vertical growth in response to a range of environmental stresses: grazing would be the obvious one but there's also wind (by itself or driving movement of one plant or plant part against another) & perhaps rain. If a plant is exposed to one of these stimuli & its stem grows shorter & thicker than in an undisturbed plant, this adaptive response would leave the plant less susceptible to future damage.
Smith's paper goes on to describe how to investigate & analyse this growth response to touch - very interesting & also very doable, if you're interested in having a go yourselves :-)