TACTILE PAPILLAE OF STAMENS 



583 



thin for some distance above their base, a feature which recalls the 

 characteristic hinge-areas so frequently developed in connection with 

 the guard-cells of stomata (cf. p. 447). This thin region, which 

 completely encircles the papilla, is quite narrow, and passes over 

 insensibly into the thicker portion of the cell-wall. In the corners of 

 the cell it frequently becomes modified so as to form a (marginal) pit 

 occupied by an extension of the protoplast (Fig. 236 b). 288 



It can hardly be doubted, that the hinge-like, unthickened area in 

 the outer wall of the sensory cells of Berberis serves to facilitate the 



A. Sensory cell with tactile papilla from the ventral surface of a staminal filament 

 of Berberis vulgaris, in vertical section. B. Another section passing through the 

 adjacent corners of two cells, to show the hinge-areas which are present at these . 

 points. C. Sensory cell from a filament of Abutilon striatum in vertical section ; 

 outer wall pushed in. 



perception of mechanical stimuli. For when the papilla is touched 

 or pressed upon from above, the thin strip of membrane at its base 

 will bend slightly outwards ; if the papilla is pushed to one side, the 

 hinge-action of the basal strip will again lead to local deformation of 

 the ectoplast. 



In Abutilon stria turn, the free upper portions of the staminal 

 filaments, which, further down, are united into a tube, are sensitive on 

 all sides, especially towards their distal extremities. Curvature takes 

 place towards the stimulated side. The somewhat elongated sensory 

 cells are distinctly papillose, especially in the terminal portion of the 



