DNA Multiplication as a Requirement for Expression of Floral Stimulus in Pharbitis nil.

It has been shown previously ( 15) that photoperiodic induction in Xanthium is inhibited by application of the pyrimidine, 5-fluorouracil (5-FU). More recently (1) it has been demonstrated that the process which is inhibited by 5-FU and which is related to the process of flowering, is the synthesis of ribonucleic acid (RNA) in the Xanthium bud during the first part of the inductive dark period. The experiments described in this paper were designed to determine if 5-FU also inhibits flowering in another short-day plant which also requires but one inductive long night, namely, Pharbitis nil, and if so, by what mechanism 5-FU exerts such inhibition. It will be shown that 5-FU completely inhibits flowering in Pharbitis by suppressing deoxyribonucleic acid (DNA) multiplication in the shoot apex.