"Mitogenetic Rays?", Nature 140:1007-1008, 11 December 1937, doi:10.1038/1401007c0 (unsigned news item; Google lists "A Hollaender" as author, the page does not). Abstract read [web] https://www.nature.com/articles/1401007c0
Content (paraphrase): reports Hollaender and Claus, NRC Bulletin No. 100, two years' work to prove or disprove mitogenetic rays (defined as 1900-2500 A, 10-1000 quanta/cm2/s). All attempts, biological and physical detectors, were negative. It notes that about six hundred papers had been published on the subject. Short quote: "all the attempts have yielded negative results."
Bearing: the main contemporary negative test, against claims 1, 2 and 7, published the year after Rahn's book. Rahn's reply, if any (for example in Tabulae Biologicae 1937 or later), is a target for the next run. Volodyaev and Beloussov (2015) dispute the study's conditions (see frontiers note).