STUDIES OF THE FINE STRUCTURE OF MICROORGANISMS IV. OBSERVATIONS ON BUDDING Saccharomyces cerevisiae BY LIGHT AND ELECTRON MICROSCOPY

The identification and characterization of the resting and proliferating yeast nucleus are sub-jects which have been extensively studied by yeast cytologists. Conflicting results have been obtained, and a noticeable lack of general agree-ment still exists. Differences are particularly apparent with respect to the presence or absence, as well as number, of cytologically demonstrable chromosomes similar in structure to those found in higher organisms. The question as to whether or not a typical mitotic process occurs, com-parable to that found in higher organisms, also has not been adequately resolved. In pointing out a few of the difficulties encountered in the in-vestigation of these problems, Mundkur (1954) states that "Incertitude and divergences of opinion of these questions have resulted partly from difficulties inherent in obtaining suitable preparations of organisms so small as yeast for cytological analysis...." A general review of the pertinent literature reveals that the limited resolving power of the light microscope and lack of suitable staining techniques have been important factors in im-peding progress in the field of yeast cytology. The use of the electron microscope to overcome the limitations of the light microscope offers attractive possibilities, and investigations utiliz-ing electron microscopy for the clarification of long standing disputes involving the fine struc-ture of the yeast cell have already yielded promis-ing results. Northcote and Horne (1952) investi-gated the structure of the yeast cell wall by means of HCl hydrolysis and electron microscopy, whereas Bartholomew and Mittwer (1953, 1954) employed prolonged exposure to ultraviolet light and electron microscopy for the investiga