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



HISTOLOGY AND CYTOLOGY OF THE PEDICEL 



1. HlSTOLOGICAL AND CYTOLOGICAL CONDITIONS OF THE 



MATURE PEDICEL 

 a. NICOTIANA 



The vascular system in Nicotiana, 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 tracheae 

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

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

 xylem 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- 



c - 



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. 



