PERSPIRATION OF PLANTS. 13 



the leaves is composed of two distinct laminse, is 

 not only proved by the presence of its vessels, but 

 particularly by the above-mentioned circumstance, 

 viz. that I was not able to dislocate these vessels 

 by the continued friction of a hair pencil. 



Having already mentioned the oblong shape of 

 the aperture contained in the middle of each recep- 

 tacle, I shall now give a fuller account of my ob- 

 servations upon these organs. Their closing and 

 opening, Mr. Von Gleichen k has already noticed 

 in the ferns. On examining a small portion of 

 this membrane under water upon the glass-slider 

 of a compound microscope, it is found, that the 

 light reflected by the mirror, makes this opening 

 appear as splendidly illuminated as the water about 

 it. Now as this is not found upon any other part 

 of the surface, it is a sufficient proof of the com- 

 pleteness of these apertures. 



Each of them when shut, represents a dark 

 coloured line, broader or narrower; but when 

 open, the two extremities run out into acute 

 angles, which make it appear like a fissure with 

 sides forming an arch. 



