PLATE 6. 



Low-power Photomicrography. 



TRANSVERSE SECTION THROUGH THE PETIOLE OF Cycas revoluta x 10 



Objective Zeiss Micro-Planar. 50 mm. F. 4.5. 



Ocular None. 



Condenser ... Back combination of Watson's Universal 



Achromatic. 



Illuminanl ... Liliput 4 amp. arc. 

 Aux. Condenser Bull's-eye, parallel beam of light. 



Screen Wratten's B (green) and G (yellow). 



Plate Imperial N.F. 



Exposure 1 sec. 



Developer ... Pyro-soda. 



Section stained with Haematoxylin and Saffranin. Lignifled tissue 

 stained red, urilignified blue. Process given on page 261. 



This is an example of low-power photomicrography for which the 

 use of a planar lens is very desirable in order to obtain a flat field. 

 The screens B and G, together giving approximately monochromatic 

 light of wave length 5100-6000, were used on account of the colour of 

 the section, and also because their transmission corresponds with the 

 colour with which the lens works to the best advantage. 



Photo. W. B. R. 



\Tofollow Plate 5 and page 48. 



