Cytokinin and growth of excised roots of Bryophyllum calycinum.

Excised roots of Bryophyllum calycinum require for growth both auxin and cytokinin. This is demonstrated by the poor growth of 2-mm root tips in a basal medium of mineral salts, sucrose, and vitamins supplemented with either an auxin or a cytokinin, and much better growth when the basal medium is supplemented with both auxin and cytokinin. However, both substances are synthesized by the root, as is demonstrated by the growth of large inocula (dry wt 6-7 mg) through many successive passages in a medium limited to mineral salts, sugar, and vitamins.