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University of California PiiNications in Botany [Vol. 5 



largely because of the ease aud regularity with which abscission is 

 induced in this hybrid bj^ sudden changes in the external environment. 



Experiment 5. — This experiment was devised to discover the effect 

 of reducing the volume of material proximal to the separation layer 

 on the abscission of flowers of Nicoiiana as induced by illuminating 

 gas. Two series of flowers were cut as in figure 9. In the last two 

 flowers represented on the right the cut was made less than 0.5 mm. 

 from the separation layer. These flowers were then rolled in damp 

 filter paper and left in 1.5 per cent illuminating gas overnight. After 

 fifteen hours, abscission had occurred in all the flowers except the one 

 represented on the extreme right in the figure. Abscission had 

 occurred in one flower in which the cut had been made less than 

 0.5 mm. from the separation layer. The control to this experiment 

 showed that abscission does not occur for several days in a series of 

 flowers cut as in figure 9 and kept under normal conditions. 



Experiment 6. — This experiment was devised to show the effect 

 upon abscission of reducing the volume of material distal as well as 

 proximal to the separation layer. In this case the flowei*s were cut off 

 at varj'ing distances from the separation layer, making the series 

 shown in figure 10. The last two pieces on the right in this series 

 were cut less than 0.5 mm. on each side of the separation layer so 

 that the total length of the pieces was not much above 1 mm. In this 

 experiment and in similar ones which follow it was necessary to keep 



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Fig. 10 



