Once, many moons ago, before I was completely distracted by children, I belonged to the Hardy Plant Society. At one of the lectures I attended, there was a landscape designer whose approach to design centered on the gardens of a client's childhood. She felt that the key elements to a successful, personalized garden lay in a gardener's early memories of color, texture, scent, vegetation, etc. (Yes, this
did, and does, sound a bit like therapy through plants.) But, as I look around my garden, I see elements of my childhood. In her garden in Michigan, my Grandmother grew many different kinds of daylilies, violets, lavender and roses. I have all of these. It is like an inheritance. The genetic desire to collect and hoard that which pleases and reminds. 
Wouldn't that be an interesting thesis? To follow a family's successive generations through their gardens; to see the correlations from era to era.