172 



PHYSIOLOGY OF NUTRITION. 



example, are closed at night. Direct sunlight causes them to 

 open widely, and if we suddenly cut off the light from leaves pre- 

 viously brightly illuminated, we shall, after a few hours, find the 

 stornata closed. We may also, as I have often done, experiment 

 with leaves of Amaryllis removed from the plant, and placed with 

 the cut end in water. If we examine sections of such leaves after 

 they have been brightly illuminated for several hours, we always 

 find the stomata open, whereas leaves which have been kept in the 

 dark exhibit closed stomata. Schaefer (I.e. p. 194) showed 

 directly that the closing in darkness is due to diminished turgi- 

 dity of the guard cells, and not to increased turgidity of the 

 neighbouring epidermal cells. In investigating the influence of 

 conditions of illumination on the stomatal apparatus of Orchis 

 mascula, I could not determine any marked difference as regards 

 width of slit between leaves exposed to light and leaves kept dark. 

 Leitgeb also has recently obtained similar results with Orchis (see 



his cited work, p. 160). 

 The influence of in- 

 duction currents on the 

 stomatal apparatus is 

 very surprising. We 

 take a strip of epi- 

 dermis from the under 

 side of a leaf whose 

 stomata can open 

 widely. I obtained 

 the best results with 

 leaves of Orchis mas- 

 cula, gathered in the 

 daytime and kept for 

 some time in water. 

 The strip of epidermis 

 was placed on a slide 

 like that described in 

 54, and depicted in 

 Fig. 45, which is de- 

 signed for studying 

 the influence of elec- 

 tricity 011 plant-cells. 

 If we focus a few 

 stomata, and then pass induction currents through the section, 



FIG. 61. Apparatus for proving 'that the air can pass 

 through stomata. 



