THE PAPILLOSE EPIDERMIS 



610 



position. The behaviour of a diaheliotropic leaf-blade has been compared 

 by Ernst Mach to that of the human eye, which is in a state of heliotropic 



Fig. 254. 



Lens-cxperinient with the adaxial foliar epidermis of Anthurium lev.coneurum, in 

 vertical light ; symmetrical illumination of the inner epidermal walls. (Microphoto- 

 graph.) 



Another lens-experiment with Anthurium leuconeurum, in oblique light ; asym- 

 metrical illumination of the inner epidermal walls, the bright areas being all dis- 

 placed towards the right. Same preparation as in Fig. 254. (Microphotograph.) 



equilibrium when the image of the object under observation (e.g. a 

 candle flame) falls upon the " yellow spot " of the retina. In this 



