1918] Kendall: Abscission of Flowers and Fruits in Solanac&ae 365 



than the walls of normal cortical cells, especially at the corners, thus 

 giving the tissue a somewhat collenchymatous appearance. The small- 

 est cells more proximal show this collenchymatous nature more strik- 

 ingly than do the others. No difference in chemical composition could 

 be detected, by means of microchemical tests using caustic potash, 

 sulfuric acid, nitric acid, and various stains, between the_cell walls of 

 the separation cells and walls of other cortical cells. Other tests, how- 

 ever, indicated a difference in the nature of the cell contents in the 

 two types of cells. Iodine frequently indicates the presence of starch 

 in these cells and also colors the protoplasts a darker brown than in 

 normal cells, showing that the separation cells are rich in protoplasm. 

 The amount of starch in the cells, however, was found to be extremely 

 variable, ranging from a total absence of starcli to an abundance of 

 it. Iodine green imparts to the protoplast of the separation cells a 

 deep blue color in contrast with other cortical cells, which are not 

 colored by this stain. The blue reaction is most prominent where the 

 separation layer crosses the phloem. Other cells which react in the 

 same way to this stain are the sieve tubes and companion cells and 

 the storage cells in the axil of the pedicel. 



b. LYCOPERSICUM 



Conditions in Lycopersicum differ in certain respects from those 

 existing in Nicotians. In the former the separation zone (fig. 2, a) 

 seems to be located at the middle of the pedicel 

 and is marked externally by a swelling, as well 

 as by the groove of the type already noted as 

 characteristic of the pedicel of Nicotiana. This 

 groove in the tomato is very deep (plate 53, 

 fig. 1), reaching fully half the depth of the 

 cortex, and is, furthermore, of about the same 

 depth all the way round, differing in this 

 respect from Nicotiana, where the groove is 

 absent or poorly developed on the ventral 

 side. The vascular system in Lycopersicum 

 (fig. 2, &), in contrast with the condition in 

 Nicotiana, is composed of scattered bundles 

 of xylem which in this case do not form a 

 crescent proximal to the groove but are in the 

 form of a complete cylinder throughout the 

 entire pedicel. Beneath the epidermis (fig. 



r ~C 



Fig. 2. Diagram of pedicel 



of Lycopersicum 

 a separation zone, 

 ft vascular system. 

 c epidermis. 

 <i separation layer. 

 e pith. 

 f chlorophyl-bearing 



tissue. 

 g collenchyma 



