510 RADIATION BIOLOGY 



mutagen induced in the egg material, as was surmised in the work on low 

 doses (p. 477), it must be noted that the two contrasted series in this 

 experiment had differed in other respects, including the age of the 

 males and the environment of the sperm, which might have affected the 

 mutational susceptibility of the paternal chromosomes. Furthermore, 

 studies of Bonnier and Liining (personal communication) on the produc- 

 tion of mosaics have shown that the condition of the egg (determined by 

 factors such as aging and radiation) can affect the manner of reunion of 

 broken chromosome pieces brought in by the sperm. This influence too 

 could therefore have affected the frequency of recovered lethals of 

 paternal origin, without its being necessary to infer that there had been an 

 effect on the frequency of either gene mutations or breaks in the paternal 

 chromosomes. 



Evidence that irradiated protoplasm exerts Uttle or no mutagenic 

 influence on nonirradiated chromosomes has been obtained in other 

 species from experiments in which the eggs were so heavily irradiated 

 that all the chromosomes of maternal origin were lost and only the 

 chromosomes derived from the unexposed spermatozoa took part in 

 development. In the resultant " androgenetic " offspring any visible 

 mutations would have been evident because of their haploid condition; 

 yet all proved to be normal. This result was obtained first in experi- 

 ments by Astaurov (1937) on the silkworm and later in more definitive 

 experiments by A. R. Whiting (1950) on the wasp Habrohracon. In the 

 latter case, it can be calculated that seven or more visible mutants would 

 have been expected among these offspring if the paternal chromosomes 

 had been directly exposed. This would not, however, rule out the possi- 

 bility of a transverse induction having a strength only a tenth or less that 

 of the more direct mutagenic effect. Moreover, in the case of all the 

 cited experiments dealing with this question the objection might be 

 raised that enough time had elapsed to allow such an influence to fade 

 away, inasmuch as the sperm did not usually enter the eggs until a day to 

 a week after the eggs had been irradiated. It would be of interest if this 

 interval could be considerably reduced. 



Experiments involving a shorter interval have been reported by 

 Kausche and Stubbe (1940) for the tobacco mosaic virus. Although 

 these investigators were unable to produce mutations by X irradiation of 

 the virus in pure solution or as a crystal and although they obtained only 

 1 mutant colony among 1200 control colonies (each colony being derived 

 from one particle), nevertheless, 3 mutant colonies were found among 

 800 when the untreated virus particles were seeded into host plants which 

 had been irradiated not more than 24 hours previously. These numbers 

 do not appear sufficient to be more than suggestive. However, the 

 investigators report further that all 3 mutant colonies in the experimental 

 series occurred in a group of 400 colonies parasitizing host plants in 



