Sexual Induction in Volvox Carteri

The study of the dependence of reactions on the concentration of various compounds is often of great value in determining reaction mechanisms . In chemical kinetics, it is often found that, according to van't Hoff's rule, the order of dependence of a reaction on the concentration of some compound involved in that reaction is equal to the number of molecules of the compound involved in each reaction event (Pannetier and Sanchay, 1967). This common equivalence has been used in biological as well as nonbiological studies . For example, the finding that the number of bacteriophage plaques is a linear function of bacteriophage concentration was used to conclude that only a single particle is required to produce a plaque (Ellis and Delbr€ck, 1939) . Similarly, the linear relationship between X-ray dose and frequency of mutation supports the view that one X-ray photon can produce a mutation (Schultz, 1936) . Chu, Giles, and Passano (1961) showed that the frequency of single-break chromosomal aberrations is a linear function of X-ray dose . However, aberrations requiring two breaks were found to occur as the square of the dose. Thus, each break appears to require only a single X-ray photon and rearrangements requiring two breaks show a second-order dependence on X-ray dose. Gall (1963) was able to infer the strandedness of lampbrush chromosomes from the kinetics of appearance of breaks upon DNase digestion . This report includes a quantitative analysis of the induction of sexuality in Volvox carteri f. nagariensis. Sexuality in this species is induced by a proteinaceous inducer (Starr, 1968 and 1970) . The inducer acts to cause the asexual reproductive cells or gonidia to cleave to form