Cytogenetic Studies in Paeonia II. the Cytology of the Diploid Species and Hybrids.

H E cytological study of the numerous species and hybrids in the T SAUNDERS collection has now been carried on intermittently for five years, during which time a considerable amount of data have been accumulated. The present paper aims to present the most significant findings in the diploid species and hybrids, particularly insofar as they help to explain species relationships in this most complex and interesting genus. The somatic chromosomes of Paeonia have already been studied by LANGLET (1928), DERMEN (1933)~ and DARK (1936), and those in meiosis of some species and hybrids by SAX (1932, 1937b, DARK (1936), and the present writer (HICKS and STEBBINS 1934). These studies have revealed not only very favorable chromosomes for a study of chromatid relationships, but also a large amount of structural hybridity. The latter subject is, of course, of prime importance in connection with interspecific relationships and species evolution, and has received particular attention in the present paper.