YALE UNIVEtiSITY

OSBORN BOTANICAL LABORATORY
NEW HAVEN, CONNECTICUT

hgu 26, 1946.

Dear Dr. Sonneborn,

Thank you for your reprints and for the literattie references

you sent earlier, They btre been, need I say, most interesting.

Numnrous other recombination types have been found in E: coli,

corrobarating the account given at Cold Spring Hartrour , and supporting

quite conclusively, I think, the hypothesis of a 'sexual' phase.
The recombination types are by no means equally prevalent in mixed cultures,

suggesting that there may be some linkages. ;cesistance to Tl, thiaminless,

and in other crosses, threonineless have,hcxvever,segregated sufficiently

clearly and independently that there must beb a genie basis to these

characters (andthe others as well undoubtedly).

IYe are sontinuing the E. coli mrk, but are studying other bacteria

now as well, having just begun, in particular with Salmomlla. In a dis-

cussion with Kimball, the analogy of phase variatton to the self-differen-

tiation of mating types in P. bursaria was pointed out. T)o you know -:;hether

anything has been done since 1942 on that problem? Ahat do you think about

it? Finally, has any attempt been made to differentiate mating tFes on a

serological basis?

Very sincerely yours,
:I
9lLkP
           .