The Effects of Light Intensity on the Ultrastructure of Chlorogloea Fritschii Mitra Grown at High Temperature¹,²,³,⁴

SUMMARY The effects of high and low light intensities on the ultrastructure of the large, single cells (designated as Stage IV cell types in the life cycle) of Chlorogloea fritschii grown at 45 C are described. The most noticeable difference between cells grown at 20–60 ft‐c and at 700 ft‐c is in the number and arrangement of the photosynthetic lamellae. In the former, the lamellae are in groups of 4–6 units, the component membranes of which are compact and, closely appressed. While the thylakoids are long, continuous, and frequently invaginated into the central cytoplasm to form concentric whorls, there is no evidence of swelling or separation to form vacuole‐like structures. In contrast, in cells grown at 700 ft‐c, the photosynthetic lamellae are fewer and fragmented, with the segments peripherally arranged dint frequently swollen and vesiculate. There are also differences in the, nature of the sheath, in the amount of cyanophycean starch, and in the cytoplasmic inclusions. At 20–60 ft‐c, the sheath, is extensive and. fibrillar; cyanophycean starch is abundant; and cytoplasmic inclusions (e.g., αand β‐granules) arc sparse. At 700 ft‐c the sheath is less extensive and frequently composed of short segments of fibrils and of particulate material; cyanophycean starch is sparse; and cytoplasmic inclusions are abundant.