Influence of Photoperiod on Water Uptake of Xanthium

The water absorption of plants of Xanthium pensylvanicum Wallr. grown in solution culture and subjected to photoinductive and non-photoinductive photoperiods was investigated. 2. Plants grown under greenhouse conditions and given continuous photoinduction exhibited peaks in absorption, in comparison with non-induced plants, coincident with the appearance of macroscopic flowers and with anthesis. 3. Plants given continuous photoinduction in the control room had a single period of accelerated water uptake coincident with meiosis. Anthesis in this case occurred after the rate of absorption had declined. 4. Aqueous solutions of indoleacetic acid in concentrations of 0.01-1000 p.p.m. sprayed on the leaves of non-induced plants did not promote water uptake. Leaf applications of 10 and 100 p.p.m. 2,4-dichloroanisol resulted in a slight stimulation of absorption. 5. Water absorption by debudded plants under photoinductive daylengths was similar to that of intact photoinduced plants. From this it was concluded that the onset of stages in the reproductive process normally correlated with accelerated water uptake is a merely parallel occurrence and not a causative factor.