4. Marigold cultures were inhibited by 400 mg/
liter of all the purines and pyrimidines. Adenine and
guanine were the most inhibiting. Some stimulation
occurred with low concentrations of cytosine, guanine,
and uracil and with ribose.
5. The antimetabolite thiouracil was strikingly inhibitory
to tobacco cultures with concentrations of 10
or more mg per liter. Marigold cultures were inhibited
by this compound only at 100 mg per liter.
6. The amounts of RNA that inhibited or stimulated
these cultures, respectively, appeared comparable
to the amounts inside stimulated dark green or
inhibited light green tobacco leaves infected with
TMV, which might clarify the characteristic mosaic
symptoms.