MANNER OF PRODUCTION OF MUTATIONS 589 



Mechanical vibrations of supersonic frequency, up to a rate of 285,000 

 per second, were tried on adult Drosophila by Hersh, Karrer, and Loomis 

 (1930). Only mutations (sex-linked or dominant autosomal) which were 

 visible by inspection of the first generation of offspring were looked for. 

 It was not possible by the methods used to demonstrate a heightened 

 rate of production of these, except for the appearance, in the offspring of 

 several treated males, of a mottled-eye character. Although in other 

 work mottled eyes have nearly always been associated with structural 

 chromosome changes that were produced by radiation, the mottled in 

 this case, unlike that found elsewhere, proved to be of a recessive auto- 

 somal nature and to have low penetrance. This, combined with the fact 

 that the same trait appeared in this case in the immediate offspring of 

 more than one treated male and in several of the offspring of some of 

 these males, indicates that the mutation had been present prior to treat- 

 ment. It is probable that in this work air interposed a barrier to the 

 transmission of the vibrations. More recently, however, Wallace et at. 

 (1948), using 400,000 vibrations per second transmitted through liquid, 

 have reported obtaining abundant chromosome changes by the treatment 

 of root tips of Allium and Narcissus and shoots of Helianthus. They also 

 state, in their preliminary note, that they have obtained lethal and 

 visible mutations and inversions by treatment of adult Drosophila. On 

 the other hand, Fritz-Niggli and Boni (1950), using supersonic vibrations 

 at 800,000 per second transmitted to immature stages of Drosophila 

 through water, and Frings and Boyd (1951) using sonics at 6000 per 

 second transmitted to adults through air, have both reported no produc- 

 tion of mutations, despite the damaging effects of the treatment on sur- 

 vival and (with the immature stages) on the developmental pattern. 



Mechanical stress applied in the form of the "pseudo-gravity" created 

 by centrifuging has also been reported to result in the appearance of some 

 chromosome fragments and other structural changes and of abundant 

 disturbances of chromosome distribution, leading to inheritable aneuploid 

 and polyploid chromosome sets, in work of Kostoff (1935a, b, 1938) on 

 varied plants {Nicotiana, Vicia, Triticum, and Crepis). It is not clear 

 whether the cases of breakage and recombinational union (supposing that 

 control material would show them really to have been increased in fre- 

 quency) were caused by a mere decrease in the probability of restitution 

 of spontaneously arising breaks or whether the frequency of breakage 

 itself had been increased. At any rate, as was pointed out by Kostoff, 

 this effect of centrifuging may also lie at the basis of the increase in 

 mutation frequency which had been observed by Stubbe (1930) in 

 Antirrhinum, after he had subjected the growing tissues to varied 

 chemicals (Chap. 7). For in all the chemical treatments, unUke the 

 controls, centrifuging had been used to assist penetration, and it was a 

 curious fact that it seemed to make little difference what chemical (even 



