Both literally and figuratively, The Sound of Music emanating from Mills Lawn on Saturday afternoon commemorated the 50th anniversary of the Yellow Springs Summer Strings and Band program started by Shirley Mullins and the late Mary Schumacher in 1964. The concert featured a 40-person impromptu orchestra, with long-time string teacher Cami Dell Grote, current co-director Dennis Farmer, ­long-time supporter Barbara Bradfute, and many alumni of the program. And for the finale, Mullins’ youngest student, Quentin Branlat, 6, played a measured and tonal “Twinkle Twinkle Little Star” on a quarter size cello while staring straight at his audience the entire performance.