1918] Kendall: Abscission of Flowers and Fruits in Solanaceae 385 



flower. As in the case of the corolla, there is no structure which might 

 be interpreted as a differentiated separation layer. Separation occurs 

 in a region of intergradation in cell shape between the spherical cells 

 of the ovary and the cells of the style, which are elongated parallel 

 with the long axis of the style. 



TIME OF ABSCISSION 

 1. REACTION TIME 



a. EEACTION TIME IN NOKMAL ABSCISSION 



The term "reaction time" is used in referring to two rather dis- 

 tinct subjects. First, we may have a reaction time represented by 

 the time intervening between anthesis and normal abscission due to 

 lack of fertilization. Second, we may have a reaction time which has 

 to do with the period between the application of the stimulus and 

 flower-fall in ' ' spontaneous ' ' abscission. The reaction times in normal 

 abscission were discussed in an earlier communication in the case of 

 two F! species hybrids of Nicotiana and their parents. The state- 

 ments there made have been repeatedly verified and in addition a 

 considerable amount of data has been accumulated in regard to the 

 time of abscission in other species of Nicotiana and in the genus 

 Lycopersicum. In the case of the former the observations were also 

 made upon the abscission of the corolla, the effect of pollination on 

 reaction time, and the reaction time in "spontaneous" abscission. 



In determining the abscission times for the hybrid F t H154 (cf. 

 page 386) , a great variation was noted in the normal reaction time. In 

 the case of the hybrid Fj H179 (cf. page 386), however, and in other 

 species or varieties investigated, very little variation in the time of 

 abscission has been noted. The range of variation in these species 

 and varieties practically always falls within two or three days and a 

 large number of observations gives identical times, as far as the number 

 of days is concerned, in the case of seven to ten flowers. There is a cer- 

 tain variation in the length of the reaction times in different flowers on 

 the same plant, but the plants of a species do not differ from one an- 

 other in their average reaction times. It was noticed that the figures 

 were approximately the same whether the averages were based on the 

 records of four or five flowers or of a considerably larger number ; 

 thus the results given in the following table may be considered con- 

 clusive. Where the number of flowers involved is less than four, 



