14 HISTOLOGY OF MEDICINAL PLANTS 
furnished above the condenser; this iris becomes available the 
instant an object is to be observed without the aid of the con- 
denser, in which case the upper iris diaphragm allows proper 
adjustment of the light. The mirror, one side plane, the other 
concave, is mounted on a movable bar, along which it can 
be slid—another convenience for the adjustment of the light. 
The microscope stage of this stand is of the round, rotating 
ELEITZ WETZLAR 
Seater aia aang Goes) eee 
Fic. 17.—Research Fic. 18.—Special 
Microscope Research Microscope 
and centring pattern, which permits a limited motion to the 
object slide. The rotation of the microscope stage furnishes 
another convenience in the examination of objects in polarized 
light, allowing the preparation to be rotated in order to 
distinguish the polarization properties of the objects under 
observation. 
SPECIAL RESEARCH MICROSCOPE 
A special research microscope of the highest order (Fig. 18) 
is supplied with an extra large body tube, which renders it of 
