Dear Hayes,

Thank you for your letter of Jan lst. I have usdd
the word heterozygous, inspite of the fact that K-12 strains
are nermally —- or should be ~ haploid , treferred to the cross

between two of them 3 on which oceasion a diploid should form
even if unstable, and lusting perhaps one only generation. It

is probably a loose use for this term,out xt I hoped it would
give an ide: of what I meant. - Have you tried if sterilizing
boti strains with streptomycin a cross is possible % You shoul
use in this case strains other than TLB,- and de: ivatives,
which to my mind are exceptional under this point of view s in
case you ure interested 1 could let you have them.

Yours sincerely