The advantages of cultured protozoa as a material for growth and nutrition studies are well known and have recently been stressed by Lwoff,l Hutner and Provasoli,2 and Kidder.3 Few investigations of cultured protists, however, have tried to correlate spontaneous or induced metabolic changes with structural alterations, although the material appears particularly suitable for such studies. It would be interesting, for instance, to know what happens to the chloroplasts which exist in some flagellates, when these protozoa are adapted to life in the dark.dark-adaptation is accompanied by the disappearance of the green pigment, a fact that undoubtedly results in important modifications in the metabolic pattern of these flagellates. This problem has already been investigated by light microscopy with the conclusion that the chloroplasts disintegrate during dark-adaptation and reform when the flagellates are brought back to light. Partly because of the limited resolving power of the light microscope, however, it has not been possible to determine whether the old chloroplasts disappear completely, or how the new ones develop.The present work represents an attempt to investigate this problem by using the high resolving power of the electron microscope and by following, in parallel, the development of the green pigments and the structure of the chloroplasts during light-or dark-adaptation.Accordingly, onty preliminary observations will be presented, most of them concerning the morphological background of the problem; i.e., the organization of the cytoplasm, chloroplasts included, as revealed by the electron microscope in the two algal flagellates we selected for our experiments.
Malerial and MethodsThese flagellates, namely Euglena gracilis var. bacillaris, and Poteriochromonas stipitata, a phagotrophic chrysomonad, proved to be very appropriate materials for experimental study due to the comparative ease of their handling, their fairly rapid growth, and the possibility of controlling the chemical and physical environment affecting their morphology and growth. These organisms can be grown in a chemically defined medium either in light, where they develop green pigment (chlorophyll) or in darkness, where they become colorless. The process is reversible, but can be made irreversible by heat7 or streptomycin treatment.'. * Both flagellates were obtained from the Haskins Laboratories$ and grown in the culture media reported by Hutner et ~1 .~. lo The organisms were grown a t room temperature (~25'C.) either under continuous
As is wellThe study is still far from complete.
Material.Culture methods.
