Nitrogen Nutrition in Relation to Photoperiodism in Xanthium Pennsylvanicum

Plants of Xanthium pennsylvanicum were grown in sand cultures containing either an abundance of nitrogen or very little. They were first grown on long photoperiod. Then all were given an induction period of seven short photoperiods and then one-half were returned to long photoperiod, the other half continuing on short. The plants continued on short photoperiod and receiving an abundant supply of nitrogen bloomed first; those of the same type at a low supply of nitrogen bloomed next; those on long photoperiod and high nitrogen supply were the third to bloom; those on long photoperiod and low nitrogen were the last to bloom. 2. Of the short day plants, those receiving an abundant supply of nitrogen produced the greatest number of staminate heads. All the plants on long photoperiod produced more staminate flower clusters than the plants on short photoperiod. The percentage of abortive pollen grains was greatest on the plants on short photoperiod. In the latter a low plane of nitrogen supply resulted in the greatest number of defective pollen grains, and in the plants on long photoperiod a high supply of nitrogen resulted in the same effect. 3. There were more fruits per average plant which received a short photoperiod than a long one. Whether the photoperiod was long or short, those given an abundant supply of nitrogen had many more burs than those given a low supply. More seeds were found on plants on long photoperiod because many of them on short photoperiod had empty burs, many of the latter developing parthenocarpically. 4. Plants grown on a long photoperiod following an induction period with a low supply of nitrogen bore fruits and were larger than control plants grown on a similar long photoperiod with no induction period but with a similar low nitrogen supply. The latter bore no fruits.