Histological Variations in Cosmos in Relation to Photoperiodism

The plants of Cosmos sulphureus Cav. var. Klondike reacting most readily to short day treatment required seven short days for the initiation of a flower primordium. The slowest plants required ten days. When the absolute minimum treatment necessary to induce flowering was given, followed by long days, there was a marked tendency toward the production of interphases between normal flowers and vegetative shoots. 2. The change of the primordium from foliar to floral was accompanied by a marked accumulation of carbohydrate and protein in the stem tip. There is a probable proteolysis and a decrease in protein in the base of the stem at the time of the conversion of the primordium to the flowering state. There is also hydrolysis of carbohydrates in the base of the stem and their removal to the stem tip at the same time. 3. The shortened light period caused a decrease of 1 per cent per day of the total materials stored. 4. There was a diurnal fluctuation of glutathione in the stem tip during the first seven days of short day treatment, but from the time of the actual anatomical shift of the primordium from vegetative to flowering the total glutathione content remained permanently higher. 5. Asparagine was somewhat higher and ammonium somewhat lower in the stem tip at the time of flower bud formation.