396 University of California PuMications in Botany [Vol.5 



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indicated above, in the case of injury to the ovary in which this organ 

 may be merely punctured, without necessarily removing any material, 

 yet abscission occurs in one to two days after the injury. 



It has, on the other hand, been evident throughout all the abscis- 

 sion experiments that age of flower is the important factor in deter- 

 mining the reaction time, older flowers nearly alwaj's responding more 

 slowly to stimulation by injury than younger ones. It will be seen, 

 however, from the tables that there are occasionally individual excep- 

 tions to the general rule. These exceptions might be explained in a 

 number of ways. For example, it is possible in the case of older flow- 

 ers that the ovary, having increased in size, was accidentally cut in 

 the operation of injury, thus adding the extra factor of stimulation 

 of the ovarj' which in younger flowers would not be present. In gen- 

 eral, such exceptions to the general rule indicate to what extent the 

 normal or abnormal physiological conditions of the plant enter into 

 the problem. 



2. Abscission Time 



The abscission time, or the actual time involved in the process of 

 cell separation, was considered in a preliminary paper (Goodspeed and 

 Kendall, 1916) wherein the minimum time in which abscission was 

 known to have occurred w^as stated to be from four to eight hours in 

 normal abscission and from one to four hours in "spontaneous" 

 abscission. A few additional data are now at hand in the case of 

 F^ H179 and Nicotiana Tahacum " ^Maryland. " These two forms, 

 as has already been noted, are a little more sensitive than most 

 Nicotiana varieties and normal abscission was found to take place in 

 from three to six hours. 



The time of cell separation in "spontaneous"' abscission can be 

 more exactly determined than that in normal abscission because of 

 the regularity with which the plants respond to certain conditions of 

 injury or to the presence of narcotic vapors. Data on this point were 

 obtained in the follow'ing manner. Flowering shoots with flowers of 

 different sizes were cut, placed in water and inserted under a bell-jar. 

 Enough illuminating gas was then introduced under the jar to make 

 1.5 per cent approximately. The temperature during the experiment 

 was practically constant at 19° C, After the shoot had been left in 

 this abnormal atmosphere for five hours a few flowers were picked off 

 at fifteen-minute intervals and free-hand sections made of their 

 pedicels until flowers about the size of those which were being sec- 



