HYDATHODES 



145 



(Fig. 71, B, left-hand figure) ; in the middle of the head there 

 is a small space between the cells, and above this the overlying 

 cuticle is pierced by a minute hole (/>.) through which the water 

 is secreted. Both here and within the leaf cavities of the Tooth- 

 wort (LathrcBa), where similar hydathodes occur (Fig. 71, C, h.), 

 glandular hairs (g.h.) of another type are present, which may 

 take part in the secretion of water. 



Fig. 71. — Water-secreting hairs. A, Runner Bean (Phaseolus multiflorus) . 

 B, Yellow Rattle (Rhinanthiis) . C, Toothwort (Lathraa squamaria). 

 The left-hand figure of B from the surface, the others in vertical 

 section, i.e., basal cell ; ^. A. , glandular hair ; /;., hydathode ; ^.,pore; 

 s.c, stalk cell. 



Another kind of hydathode, exhibiting quite a different 

 mechanism, is much commoner among British plants. These 

 hydathodes are not hair-like, but occur generally above the 

 bundle-endings, being especially located at the leaf-apex (Grasses) 

 or on the tips of the leaf-teeth (Lesser Celandine). In all these 

 cases the water escapes from so-called water-pores, which are 

 situated in the epidermis of the hydathode (Fig. y^- St.) and 

 resemble ordinary stomata, except that they are often larger 

 and that their pore remains permanently open in correspondence 

 10 



