Abstract
The cells of Navicula pelliculosa (Bréb.) Hilse, when grown in media which contained 3.5, 8.3, and 34.0 mg. Si per liter, reproduced with generation (doubling) times of 20.4, 13.7, and 13.1 hours respectively. The degree of silicification of the cells in each culture initially fell with increasing population. After exponential growth had ceased, this value varied between 0.8 × 10−9 and 2.2 × 10−9 mg. Si per cell, depending on the amount of silicon originally present in the medium and on the age of the culture. When placed in a fresh silicate solution, the cells took up additional silicate with increases in silicon content of 50%, 90%, and 15%, respectively. Silica (SiO2) may represent from 4% to 22% of the dry weight of the cells. The average thickness of the frustules has been calculated to range between 200 and 600 Å.

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