1918] Kendall: Abscission of Flowers and Fruits in Solcnaceae 363 



HISTOLOGY AND CYTOLOGY OF THE PEDICEL 



1. Histological and Cytological Conditions of the 

 Mature Pedicel 



a. NICOTIANA 



The vascular system in Nicotian-a, as in all the other genera 

 examined, is characterized by intraxylary phloem. Nicotiana differs 

 slightly from all others in that the xylem seems in cross-section 

 to be composed of a continuous ring of radial strands of trachea? 

 rather than composed of a broken ring of distinct bundles. When a 

 branch of the vascular system (fig. 1, a) containing twenty to thirty 

 xjdem strands is given off to the pedicel, it assumes the shape of a 

 crescent in cross-section, with the opening of the crescent on the ven- 

 tral side. A short distance distal to the groove which marks the sep- 

 aration zone (fig. 1,6), the crescent closes and throughout the 

 remainder of the pedicel the vascular system forms a complete cylin- 



Fig. 1. Diagram of pedicel of Nicotiana 



a — vascular system. 

 b — separation zone. 

 c — pedicel cortex. 

 sc — stem cortex. 

 e — epidermis. 



f — chlorophyllous tissue. 

 g — groove. 

 h — separation layer. 

 p — pedicel pith. 



