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 (p.) through which the water 

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

 wort (Lathrcea), 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. 



.C. 



E.J.S. 



F IG . 71. Water-secreting hairs. A, Runner Bean (Phaseolus multiflorus). 

 B, Yellow Rattle (Rhinanthus) . C, Toothwort (Lathrcea squamaria). 

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

 section, b.c., basal cell ; g.h., glandular hair ; h., hydathode ; p., 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. 73, St.) and 

 resemble ordinary stomata, except that they are often larger 

 and that their pore remains permanently open in correspondence 

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