488 



SECRETORY AND EXCRETORY SYSTEMS 



may confine our attention to those epidermal hydathodes which do not 

 communicate directly with the water-conducting system ; these always 

 correspond either to modified epidermal cells or to multicellular 

 trichomes. 



In Gonocaryum pyriforme (Icacinaceae) numerous unicellular hyda- 

 thodes are interspersed among the ordinary epidermal cells on both sides 



Flu. 193. 



Unicellular hydathodes. A and B. Gonocaryum pyrifonne. A. Hydathode in L.S. 

 B. Hydathode in surface view. C-E. Anamirta cocculus. C. Hydathode in L.S. 

 D. Papilla more highly magnified, showing the mucilaginous tip. E. Papilla with 

 tip open. 



of the leaf. Each water-secreting cell consists of three portions 

 (Fig. 193 a.). The thick outer wall is produced outwards into a 

 small oblique papilla, the extreme tip of which is of a mucilaginous 

 consistency. This papilla is traversed by a narrow longitudinal canal, 

 which communicates with the cell-cavity at its inner end ; at its other 

 extremity the canal ends blindly in the distal cap of mucilage, or, if the 

 latter has been washed away by rain, opens directly to the exterior. 

 The papilla thus constitutes the outer opening of the hydathode. The 

 central and largest portion of the hydathode is shaped like a four- to 

 six-sided funnel. At an early stage of development, the internal 

 aperture of this funnel becomes surrounded by a stout projecting 

 flange of cellulose ; later on its lateral walls also undergo a considerable 

 amount of thickening; like the flange and the outer wall, they are strongly 



