PLATE 5. 



Low-power Photomicrography. 



TRANSVERSE SECTION THROUGH THE FLOWER BUD OF SALSIFY x 9, 



stained with Borax carmine. 



i 



Objective 3" Achromat. 



Ocular None. . 



Condenser ... Back combination of Watson's Universal. 



Illuminant ... 4 amp. arc. 



Aux. Condenser Double convex, giving parallel beam. 



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



Plate Imperial N.F. 



Exposure 2 sec. 



Developer ... Pyro-soda. 



The section shows the structure of the inflorescence of the 

 Composites, consisting of a number of individual florets, surrounded 

 by an involucre of bracts. 



An example of low power photomicrography, in which the use of 

 the back combination of an achromatic condenser is to be noted as the 

 illuminator employed with an ordinary 3" achromat. Good definition 

 and contrast are ensured by using monochromatic light of wave 

 length 4600 to 5100. The objective has sufficient covering power and 

 flatness of field for an object of this type, but a micro-anastigmat is 

 generally to be preferred. 



Photo. W. B. R. [To follow page 48. 



