ELEMENTARY PHOTO-MICROGRAPHY. PLATE IV. 



WITH DARK GROUND ILLUMINATION. 



Fig. 18. Diatoms. No eyepiece, i in. objective at 2iin. Slow 

 plate. Ten minutes. 



WITH POLARISED LIGHT. 



Fig. 19. Brucine. No eyepiece, ain. objective at 24in. Chro- 

 matic plate. Ten minutes. 



