Abstract
1. Three different species of marine centric diatoms are used for physiological and biochemical studies:Cyclotella cryptica (7–13 µ valve diameter),Thalassiosira fluviatilis (14–24 µ valve diameter) andCoscinodiscus asteromphalus (60–220 µ valve diameter). 2. The shortest possible doubling time of these species under optimal cultivation conditions is: 5 h forCyclotella cryptica (300,000 cells per ml); 8 h forThalassiosira fluviatilis (10,000 cells per ml); and 24 h forCoscinodiscus asteromphalus (50 cells per ml). 3. In cultures ofCoscinodiscus asteromphalus growth curves have been obtained for cells of different stages of the meiotic life cycle, i. e. with different valve diameters (200 µ, 140 µ, 100 µ). The species and the group specific differences are discussed with the object of illustrating the factors which produce the shortest possible life cycle. 4. Silicoborate (the first growth factor composed of 3 elements without carbon) is shown to be essential for the growth of a clone ofCyclotella cryptica in a highly purified medium. Another special growth factor is essential for optimal growth ofThalassiosira fluviatilis. 5. The conditions for maximum storage of protein, lipid and carbohydrate inCyclotella cryptica are compared with the conditions which allow maximum production of these components per unit time.
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