II GERANIACE^ 137 



the leaves of 0. Acetosella consists of three layers. 

 The upper one consists of more or less blunt cones, 

 the two lower ones of star-shaped cells, leaving large 

 intercellular spaces between them. Some healthy leaves 

 were laid flat on a plate and exposed to the rays of 

 the sun falling perpendicularly on them. By pouring 



Fig. 80. — Longitudinal section of leaf-stalk and motile organ, ibh, of one of the 

 leaflet'? of Oxalis oarnea in the day position, p, epidermis of leaf-stalk; //, 

 midrib of leaflet ; G (?, vascular bundles ; m, pith of leaf-stalk. 



fresh water over them the leaves were prevented from 

 becoming too warm. Other leaflets were protected 

 from the direct rays of the sun by means of paper 

 shades. After an hour the marked leaflets were placed 

 in alcohol in order to fix the cell-contents in their 

 natural position. The decolorised leaflets were so 

 transparent that mere observation with transmitted 

 light was sufficient to demonstrate the diff"erent dis- 



