When grown under white light the elongation of WT plants is inhibited. Tall mutants not inhibited by light can therefore be easily detected. This procedure has been used successfully to isolate mutations in several of the phytochrome genes which control various aspects of photomorphogenesis (Reed et al., 1993). Eight plants out of 30,000 screened had long hypocotyls and were transplanted but only one survived. This low survival rate was probably due to damage incurred during transplantation. Mutant MCW-1 displayed several characteristics similar to the hy3 mutants which are defective in the phytochrome B gene (Reed et al., 1993). Stems of MCW-1 were longer than those of WT when plants were grown under white and blue light, and were shorter than WT when grown under green and red light (Figure 3.1). In addition, leaves of MCW-1 were pale green and did not curl downward at the edges (Figure 3.2). Crosses between MCW-1 and hy3 could be used to determine whether the mutations are allelic. Seeds of many mutant lines are available from the Arabidopsis Biological Resource Center at Ohio State University.