Cytological studies in oenothera with special reference to the relation of chromosomes to nucleoli

Abstract

Compared to the vast amount of work done on the cytology of this group of plants very little attention has been paid to a systematic analysis of the somatic chromosomes. The necessity of such a study was felt long ago by de Vries and Boedijn (1923, 1924), who tried to analyse the chromosomes of Oenothera Lamarckiana and its several mutants. Since then the somatic chromosomes of Oenothera species have been illustrated from time to time but detailed observations in this connexion remained to be made. Such a situation has probably arisen from the fact that geneticists realized that information from such a study would not throw much light on elucidation of their genetical observations, as all the species of Oenothera showed a stable chromosome number of 2 n = 14, without any significant variation in their morphology. Probably a more important factor explaining the dearth of literature on this subject is the technical difficulty involved in getting good cytological preparations of root-tips of Oenothera species. A new line of research has been opened up since the relation of Sat-chromosomes to nucleoli was discovered by Heitz (1931 a , b ) and McClintock (1931, 1934). The application of their theory regarding the corre­spondence of the number of nucleoli to the number of Sat-chromosomes is throwing considerable light on the understanding of relationship and probable origin of some of the different groups of plants. In view of these facts, a study of the somatic chromosomes of Oenothera species in relation to nucleoli was thought extremely desirable. Considerable difficulty has been overcome by the recent discovery of a method described by Semmens and Bhaduri (1939) and Bhaduri (1938), by which the chromosomes and the nucleoli can be stained differentially. The present study is part of a contemplated exhaustive study of the chromosomes in different species of Oenothera as well as other related genera.