Two years ago my attention was first called to the sensitiveness of the stamens of Portulaca grandiflora, by observing a peculiar motion in them, while a small wild bee was engaged in gathering honey, and perhaps pollen, from the flowers. Upon trial I found that I could, by touching the stamens, make them move through quite considerable arcs of circles. I pursued the investigation somewhat farther at the time, but on account of a pressure of work was compelled to drop it. Last year I again made some examinations which confirmed my previous observations, but declined calling special attention to the facts until I had had opportunity for examining Claytonia as well. This last I have been enabled to do this spring, and having now again verified my observations on the Portulacas can give the results.