1918] Kendall: Abscission of Flowers and Fruils in Solanaceae 401 



the material moist. This was accomplished in various ways, but the 

 best method was found to consist in placing the pieces on a long strip 

 of filter paper one end of which rested in water. In this experiment 

 abscission occurred after ten hours subjection to 1.5 per cent illum- 

 inating gas in all except the two pieces represented in the extreme 

 right of figure 10. Abscission here took place in several pieces rang- 

 ing from 1 mm. to 2 mm. in length. A microscopic examination of the 

 separation surfaces indicated that the process of abscission corre- 

 sponded entirely with normal abscission as it occurs in plants in the 

 field. Experiments made in a similar manner upon N. Tabacum 

 "Maryland" and Lycopersicum gave similar results. In the control, 

 which consisted in keeping pieces of the pedicel as shown in figure 10 

 under normal atmospheric conditions, abscission occurred after about 

 twenty hours, evidently as the result of no other stimulus than that 

 caused through cutting off the flower by severing the pedicel. The 

 reaction in the control, however, is much slower than in the case in 

 which the added effect of the illuminating gas is operative, indicating 

 that the latter factor, although it here serves merely to hasten the 

 abscission process, has an effect of some kind on the tissues at the 

 base of the pedicel. 



Following these two experiments, a number of attempts were made 

 in the same way to induce abscission in longitudinal free-hand sections 

 of the pedicel cut for microscopical examination. It was soon discovered 

 that the abscission process could be induced in the separation zone in 

 thick longitudinal sections of the pedicel by subjecting them to high 

 percentage (5 to 7 per cent) of illuminating gas. Cell separation in 

 cross-sections through the separation zone could not be induced by any 

 means at hand. The following experiments give more detailed results 

 in this connection. 



• Experiment 7. — In this experiment, median, longitudinal sections 

 of varying thickness were cut through the pedicels so that the plane 

 of the sections corresponded with the plane formed by both the 

 pedicel and the main axis of the inflorescence. These sections were 

 subjected to 7 per cent illuminating gas, care being taken to keep them 

 moist, but not submerged, throughout the entire experiment. The 

 best arrangement was found to be one in which the sections rested in 

 a thin film of water on one side but were exposed to the air on the 

 other. After several hours in the 7 per cent illuminating gas, abscis- 

 sion started in the thicker sections but not in the thinner ones. The 

 extent to which abscission proceeded depended upon the thickness of 



