Experiments were conducted to determine the interrelationship between the flowering ofCuscuta campestrisYuncker, a species of the parasitic angiosperm dodder, and the flowering of the short‐day plantsXanthium pennsylvanicumandGlycine maxvar.Biloxiand the long‐day plantsMatricaria parthenoidesandHyoscyamus niger.It was found that dodder flowered only on the host plants which were themselves flowering. The flowering pattern of the host plant appeared to be unaffected by the parasitism of dodder. When nonflowering dodder was introduced to soybean plants which were under noninductive photoperiods, neither dodder nor soybean flowered; but when the soybean plants were then completely defoliated, the dodder on 7 of 9 host plants began to flower. This result indicated the possibility that under noninductive photoperiods the leaves of the host plant produced a substance which inhibited the flowering of the dodder. Other experiments involved the use of soybean plants which had been linked together with bridges of living dodder. One member of each soybean pair was kept on inductive short photoperiods while the other member was kept on noninductive long photoperiods. No transmission of a flowering hormone from the induced member of each pair through the dodder bridges to the noninduced member of the pair could be demonstrated. The results, instead, support the concept that a flowering‐hormone inhibitor is translocated from the noninduced soybean partner to the induced soybean partner via the dodder bridges since the induced partners show a definitely weaker flowering pattern than corresponding photoinduced control plants.