Tricyclic nitrogenous compounds having strong plant growth regulating properties are disclosed. The compounds display the general formula wherein A is one of several nitrogen-containing radicals, R1, R2, R3 and R4 are selected from various recited aliphatic, aryl, araliphatic and heterocyclic groups. R3 and R4 may also together form one of a number of nitrogen, sulfur and oxygen containing radicals. These compounds have a variety of uses, including the reduction of plant growth height without harm to the plant.