This Fifteenth Symposium of the Society for the Study of Development and Growth is divided into three parts. In the first group of chapters T. T. Puck discusses the methods of deriving cultures from single animal cells; R. Dulbecco, problems of virus reproduction; and R. M. Klein, the current status of cultivating plant tissues. D. M. Prescott then examines the rhythmic growth and division of Amoebae; C. S. Pittendrigh and V. G. Bruce contribute a review of their analysis of internal clocks in animals; and E. Bunning writes on diurnal rhythms in vascular plants. Finally H. Gaffron and B. L. Strehler discuss the origin, significance and mechanics of photosynthesis while H. F. Blum and H. Shapley take up other aspects of biochemical evolution. Originally published in 1957. The Princeton Legacy Library uses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These editions preserve the original texts of these important books while presenting them in durable paperback and hardcover editions. The goal of the Princeton Legacy Library is to vastly increase access to the rich scholarly heritage found in the thousands of books published by Princeton University Press since its founding in 1905.