18 HISTOLOGY OF MEDICINAL PLANTS 



If the Bertrand lens is shifted out of the optical axis, one can 

 observe the preparation placed iij)on the microscope stage and, 

 depending on its thickness or its double refraction, the inter- 

 ference color of the specimen. This interference figure is called 

 the orthoscopic image and, accordingly, one speaks of the micro- 

 scope as being used as an "orthoscope." 



After the Bertrand lens has been introduced into the optical 

 axis, the interference figure is visible in the back focal plane of 

 the objective. Each point of this interference figure corresponds 

 to a certain direction of the rays of the preparation itself. This 

 arrangement permits observation of the change of the reflection 

 of light taking place in the preparation, this in accordance with 

 the change of the direction of the rays. This interference figure 

 is called the conoscopic image, and, accordingly, the microscope 

 is used as a "conoscope." 



Many types of polarization microscopes have been con- 

 structed; those of a more elaborate form are used for research 

 investigations; others of smaller design for routine investigations. 



