510 



SECRETORY AND EXCRETORY SYSTEMS 



(Fig. 206 b). The passage arises from a single tubular protodermal 

 cell, which pushes its way actively into the tissue of the leaf for a time, 

 but finally degenerates (Fig. 206 a). The cavity of this cell occupies 

 the future position of the passage, but the latter also undergoes 



Fig. 20<). 



Extra-floral nectaries of Fagraea. A. Nectary of F. fragrant at an early stage of 

 development, in vertical section ; the cavity of the enlarged tubular protodermal cell 

 becomes the secretory passage of the nectary. B. Fully-developed nectary of F. 

 lunceolitta, in vertical section. (Both figs, after Ziminermann.) 



a certain amount of independent enlargement at a later stage. This 

 type of extra-nuptial nectary thus has some points in common with the 

 septal nectaries which have already been described. 



In accordance with their function, extra-nuptial nectaries continue 

 to secrete nectar for a much longer time than nuptial nectaries, which 

 are indeed generally quite short-lived structures. Moreover, washing 

 with water does not affect their secretory activity to the same extent 

 as it does that of floral nectaries. This point was demonstrated 

 experimentally by Schimper in the case of Cassia neglecta, and the 

 author has himself obtained confirmatory results with Vicia sepium. 

 Thus, while the process of secretion is essentially the same in both types 

 of nectary, the exudation of sugar continues for a longer period in 

 the case of the extra-nuptial organs. 



In all probability the majority of nectaries are phylogenetically 

 derived from hydathodes, just like the digestive glands of carnivorous 

 plants : both the epithem- and the trichome-types of hydathodes 

 have been modified in this direction. In Vicia sepium, for example, 



