1918] Kendall: Abscission of Flowers and Fruits in Solanaceae 369 



of the flower. They are at this time rectangular in shape, elongated 

 perpendicularly to the long diameter of the pedicel, and arranged in 

 longitudinal rows. In later stages, however, when the flower is at 

 anthesis, or the fruit is forming, these cells have rounded up and 

 become irregularly arranged, thus leaving rather large intercellular 

 spaces. 



b. NICOTIAN A 

 The separation zone develops in Nicotiaua much as it does in 

 Lycopersicum. It was observed in very young buds — calyx 2 or 3 mm. 

 or shorter — that no groove was present. In buds larger than these, 

 the groove and small size of the separation cell is apparent, appearing 

 first on the dorsal side of the pedicel. It is evident that in both these 

 genera the groove and area of small cells are explained in the same 

 way, i.e., by the fact that the normal cortical cells increase in size 

 faster than do the cells of the separation zone. Since in both genera 

 abscission can occur even before differentiation of any kind appears at 

 the base of the pedicel, it is evident that the groove and small-celled 

 region do not necessarily bear any relation to abscission. This state- 

 ment is borne out by the fact that in Datura neither the groove nor 

 the area of small cells is present and in Nicotiana separation occurs a 

 short distance distal to the groove. 



c. CONCLUSIONS FROM THE STUDY OF THE DEVELOPMENT OF 



THE SEPARATION ZONE 



In view of the above discussion it is clear that the separation layer 

 in Lycopersicum, Nicotiana, Datura, and probably in the other genera 

 noted, originates according to the first method, a, proposed by Kubart 

 (cf. page 350). That is to say, the separation layer represents merely 

 a portion of the primary meristem which retains its original physi- 

 ological capacities. 



4. Increase in Size and Development of ]Mechanical Tissues in 

 THE Pedicel of Nicotiana and Lycopersicum 



There is a marked increase in the size of the pedicel in both 

 Nicotiana and Lycopersicum during the development of the fruit. It 

 was found that during this development the diameter of the pith 

 remains about the same, the actual increase in size being almost 

 entirely confined to the cortex (cf. figs, 3, 4, and 5). This increase in 

 the diameter of the cortex in the pedicel of Nicotiana is due, in the 

 first place, to an increase in the size of the original cortical cells, 



