Because it moves so fast, it is called 'the sensitive plant,' "" explains Selsam, who begins with other examples of plant movement (such as folding up at night), then notes that ""few can equal the mimosa. . . in its power to move."" Oddly, she never compares this ""power"" with the concept of locomotion traditionally listed as a distinguishing characteristic of animals. What she does is show, with Wexler's help, how the plant reacts--drooping markedly, rapidly--to touch or heat; and she explains that ""some sort of signal"" travels through the plant, causing liquid to leave the swollen ""pulvinus"" at the base of each leaf or leaflet--no one is sure whether the signal is electrical, chemical, or what. The mimosa's growth and the process of fertilization are worked into the closing suggestions on how you can have ""fun"" with the mimosa at home. Inessential, though Wexler's photos help support the impression that the mimosa's visible reactions are something remarkable.