406 University of California Publications in Botany [Vol. 5 



The general results of these observations are in a sense negative 

 and seem to indicate that the walls of the separation cells are no more 

 subject to hydrolysis than the walls on either side. This, of course, 

 does not preclude the possibility that a difference exists which is too 

 slight to be detected. It appears, however, that the general region 

 at the base of the pedicel may be more subject to hydrolysis than the 

 more distant portions. 



3. Induction by Mechanical Injury 



The results of experiments on the induction of abscission by mechan- 

 ical injury are recorded in tables 2, 3, 4, and 5, which have already 

 been considered under the heading, "Time of Abscission" (page 384). 

 Several facts of interest brought out by table 2, which deals with 

 Nicotiana Langsdorffii var. grandiflora, are summarized below. 



1. It appears that removal of or injury to the capsule does not 

 cause abscission in mature fruits (table 2, a, b, and h; table 3, c and 

 d) . The same types of injury generally do cause abscission in im- 

 mature fruits. 



2. It seems that a transverse cut completely through the flower at 

 the distal end of the calyx causes abscission only in buds or flowers 

 near anthesis (table 2, c). It appears, however, that such a cut 

 proximal to the distal end of the calyx causes abscission in flowers 

 several days past anthesis as well as in buds (table 2, a, b). 



3. Removal of the entire calyx causes fall in very young buds only 

 (table 2, d). 



4. It seems that slitting both the corolla and calyx longitudinally 

 on both sides from tip to base does not induce abscission even in young 

 buds (table 2, e). 



5. Entire removal of the style or stamens causes fall only in young 

 buds (table 2, / and g). 



6. It appears that injuries to the pedicel do not cause abscission, 

 provided the flower is not entirely cut away (table 2, z). Just here it 

 is worth mentioning that two of the pedicels cut transversely as 

 recorded in table 2, i, were cut so deep that the flowers bent over 

 and hung only by a few vascular strands and cortical cells. The 

 wound healed over, however, and the two flowers matured with the rest. 



7. It is evident that injuries which reach the ovary are much more 

 effective in causing abscission than injuries affecting the other parts 

 of the flower (table 2. b and e). 



