CHROMOSOMAL VESICLES AND THE STRUCTURE OF THE RESTING NUCLEUS IN PHASEOLUS. J. McA. KATER, ST. Louis UNIVERSITY SCHOOL OF MEDICINE. In 1885 Rabl formulated a theory which is essentially our modern theory of continuity of chromosomes. Since that time cytologists and geneticists have very thoroughly discussed this problem, with its bearing on our conception of the structure of the nucleus and the related problems of genetics. Unfortunately, even at the present time, a large part of the evidence for the individuality of chromosomes is purely inferential; consequently the subject still rests on a rather hypothetical basis. Only in one case have the chromosomal vesicles with clear outlines been traced through the resting nucleus and in this instance the condi-tions were such that the observations cannot be applied to other forms with any degree of safety (Richards, 1917). Other workers have identified chromophilic bands in the resting nucleus as chromosomes, but the outlines of the vesicles were not visible (Sharp, 1914; Wenrich, 1916). In addition to the above isolated cases a great deal of strong inferential evidence for the indi-viduality of chromosomes has been accumulated (Boveri, Conklin, etc.). While engaged in studying the cytological changes accompany-ing the ripening and germination of the seeds of the common bean, Phaseolus vulgaris, a number of observations were made which indicated that Phaseolus affords favorable material for studying the reconstruction of daughter nuclei and interpreting their resting structure. This material was even more promising because of the fact that the resting nucleus of Phaseolus is quite similar to that of some other plants. I wish to express my gratitude to Mr. G. T. Kline, artist, St. Louis University School of Medicine, for his skillful preparation of the plates, and to Professor Albert Kuntz for kindly reading the manuscript. 209
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