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Many cell types will grow when attached to a rigid surface but not in suspension, a phenomenon termed „anchorage dependence”︁. Anchorage dependence can be studied

by incorporating solid particles of varying size into gels. It has been found that colonies will form on glass fibrils 500 μ

in length, but not in the presence of silica fragments smaller than the cells. This shows that the suspending medium is not

itself inhibitory, and confirms the requirement for a rigid surface of adequate size.

The state of inhibited cells in suspension culture was examined by dispersing them in a methyl cellulose gel, in vessels

lined with agar. In this system aggregation is prevented and the cells may be recovered quantitatively. Normal, as well as

transformed, cells increase in size, and a proportion synthetize DNA during the first 24 hours in suspension culture. Growth

and DNA synthesis in normal cells then virtually cease, while transformed cells continue to grow into colonies. The

stationary normal cells remain competent for further growth for at least a week in suspension. When such cells are allowed to

attach to a rigid surface in the presence of colchicine, DNA synthesis occurs and is followed by mitosis. These results

indicate that suspended cells are blocked between mitosis and the end of the S phase of the cycle.