Dsy+mt of Genetica, Univereijqy
      Hadison 6, lllfscondn

Dr. D. Lewis,

of Wisconsin


                      !

    Jqe 2j,> 1951
                      -.i



                       _ .

John Innes Horticultural Imtitution,
Bayfordbury, Hertford, Herts.,
        Eag3a~.

Dear Dr. Lewir :

  The &lst annual repEm& of your in8titution was juat
received here, and I wa8 especially interested to read
the tantalizingly condensed 8ummary of your experience8
with mutations at the S locma,  An explanation cam to
ay mind for the ~?mporary%mutations which I hoped you
might co-t upon.

  My Botany is none too iwe, but if I am not too far off,
the mature pollen grain in Oe. organensis aontaina two
nuclei- one the tube nucleus, the other a generative nucleus
which divide8 in the pollen tube or earlier to produce the
two 8p8rm. Is it not likely that the phenotype of the
nale gsmetophyte i8 aontrolle~ by the tube nucleus rather
than the gsnerative? If ao> a eutation occurring arubraquent
to meioai.8 might produce a change enabling I@ the pollen grain
carrying the mutated allele to paas the incompatibility eieve",
although there would be no alteration detectable in the next
generation. This would not account for the remarkable family
referred to pn p. 16, lines&-10.

`phi8 notion would, however, also account simply for
the surplus of clones of single `xutants referred to in your
paper on spontaneous& autation rates, since such clones would
result either from mutations at the last meiotic! or the first
postmeiotic mitosis. Half these clonee, however, would have
to carry %-mporarytl mutations, whereas such mtationr should
not be characteriatia & larger cluster8 presumably resulting
from premeiotia mutations.

  Joshua bderberg,
Associate Professor of
    Gene tics