Abstract

Arabidopsis thaliana is a small cruciferous weed which grows naturally, mainly in Europe. Because of its qualities of small size, rapid growth, low chromosome number and self‐fertilisation, I adapted it to aseptic growth in purified agar in sterile test‐tubes. I found that it secreted various substances into the medium, but not in type or amount likely to interfere with the expression of biosynthetic mutants. Following X‐irradiation of seed, I obtained a number of mutants, including several lethals. One lethal mutant I discovered to be deficient in thiamine synthesis. It was the first biosynthetic mutant to be found in flowering plants.