Observations on the cytology and ultrastructure ofChlorobotrys regularis(West) Bohlin with special reference to its position in the Eustigmatophyceae

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Abstract
The cytology and ultrastructure of Chlorobotrys regularis is described from material in culture. The several chloroplasts previously described for this species have been found to be the lobes of a single much-divided chloroplast and the presence of pyrenoids is demonstrated for the first time. The pyrenoids are large and polyhedral in shape and are joined to the face of the chloroplast by only a narrow stalk; they are not penetrated by chloroplast lamellae or thylakoids and are surrounded by flattened vesicles, the contents of which appear finely lamellate after fixation. The layers of fibrillar mucilage surrounding the cells are separated by tripartite membrane-like structures and appear to be formed by the expansion of the cell wall material after division. The cell wall is apparently not silicified as previously described, but probably contains a high proportion of pectic substances. Chlorobotrys regularis is transferred from the Xanthophyceae sensu stricto to the new class Eustigmatophyceae mainly on the basis of pyrenoid structure and the absence of a girdle lamella from the chloroplast. Its taxonomy and possible confusion with C. polychloris is discussed.