PLATE 44. 



Medium and High-power Photomicrography 

 of moderately thick sections. 



A Fritillaria imperialis, LONGITUDINAL SECTION OF ROOT x 420, showing 

 nuclear division. 



B SECTION THROUGH FERTILIZED EGG OF Ascaris megalocephala x 1200 

 First cleavage after fertilization. 



A B 



Objective Leitz -L" oil immersion. N. A. 1.30. 



Ocular ... ... None. Zeiss projection x 4. 



Condenser ... Watson's Holos. immersion. Stopped down 



to N.A. 0.8. 



Illuminant ... Liliput 4 amp. arc. 



Aux. Condenser Double convex lens, adjusted for parallel light. 



Screens Wratten's B (green) B (green). 



and H (blue). 



Plate Imperial process. 



Exposure 1 min. 1^ min. 



A Several stages in nuclear division can be made out in this 

 figure. Nuclei with the chromatin in a reticulum, others in which 

 the chromosomes are differentiated; an equatorial stage where the 

 chromosomes are grouped in the middle of the cell, and also stages 

 at the completion of nuclear division in which the new cell wall can 

 be seen separating the daughter nuclei. 



B The chromosomes are arranged at the equator, the nuclear 

 spindle is shown, also the centrosomes at the poles. 



Both these sections were a trifle thick, but sufficient depth of focus 

 was obtained by restricting the aperture of the condenser. It is 

 generally advantageous to use a lower power objective with smaller 

 N.A. and increase the camera extension until the necessary mag- 

 nification is obtained, when considerable penetration is required. 



Photos. W. B. R. [To follow page 262. 



