Letter from Ronald Aylmer Fisher to D C Martin, concerning two papers: 'The adaptive significance of heterokaryosis in wild pencillium' by J L Jinks, and 'The variation mechanism in pencillium heterokaryosis' by J L Jinks and H Rees Paper reference code: B8 and B9 Fisher writes: 'Dear Martin, Thanks for sending me the revised version of Jinks and Jinks and Rees. The introductory remarks now do a great deal to make the subject more intelligible. Yours sincerely, R.A.Fisher'. Written at Department of Genetics, University of Cambridge, Whittingehame Lodge, 44 Storey's Way, Cambridge [England]. [Published in Proceedings B, 1952]. Endorsed on recto as received 23 April 1952. 21 April 1952