The origins of Screaming Trees?

Here's a famous photograph of pulp fiction author and Scientology creator L. Ron Hubbard holding a tomato plant connected to an E-Meter.  Hubbard claimed in 1968 that tomatoes would "scream when sliced," as detected by the E-Meter. [UPDATE: The photo appeared in "30 Dumb Inventions" on Life magazine's website, attributed to the Evening Standard of January 1, 1968, but the claims and the photo appear to be from 1959, see below.]

Hubbard was likely inspired by Cleve Backster, who had made similar claims based on connecting plants to a polygraph starting in 1966.  Backster published his claims in the Journal of Parapsychology in 1968, and his work was subsequently popularized in the 1973 book, The Secret Life of Plants.

I wonder, however, whether the inspiration for both of these crackpots came from a piece of fiction in the September 17, 1949 issue of The New Yorker--Roald Dahl's "The Sound Machine," which is reprinted in numerous short story collections, including his volume Someone Like You (1973). In this tale, a man named Klausner, obsessed with sounds beyond the ability of human beings to hear, builds a machine to convert higher pitches into human-audible sounds.  He discovers, to his horror, that plants and trees shriek with pain when cut.

Does anyone know of any documented references from Hubbard or Backster to Dahl?  Or is there another common ancestor I've missed?

My title includes a reference to the Seattle-area grunge band, Screaming Trees, whose Wikipedia entry doesn't comment on the origin of their name--but Dahl's story seems a likely inspiration there, too.

UPDATE (6 February 2013): It looks like the Hubbard photo pre-dates Backster, and was likely taken in 1959 or 1960!  It prompted a feature titled "PLANTS DO WORRY AND FEEL PAIN." in the December 18, 1959 Garden News.

UPDATE (10 February 2013): David Hambling's "The Secret Life of Plants" in the December 2012 issue of Fortean Times (p. 18) points out that Charles Darwin's 1880 The Power of Movement in Plants suggested that plants have something like a nervous system, and that Jagadish Chandra Bose published a 1907 paper on the electrophysiology of plants.  He puts Backster before Hubbard, making the same mistake of dating Hubbard's claims by the Life magazine photo caption.

Backster, by the way, was inspired by Bose's work.  He says that he started his work with plants on February 2, 1966, as reported in the introduction of his "Evidence of a Primary Perception in Plant Life," International Journal of Parapsychology, Vol. X, No. 4, Winter 1968, pp. 329-348.

UPDATE (21 October 2021): On a 1966 episode of the Joe Pyne Show, in discussion with Lewis Marvin, Pyne asserted that it has been scientifically proven that tomatoes scream when cut, likely referencing Backster.

UPDATE (5 December 2022): Not sure how I missed including the Jack Handy "Deep Thoughts" that goes: "If trees could scream, would we be so cavalier about cutting them down? We might, if they screamed all the time, for no good reason."