148 



BACTERIA IN RELATION TO PLANT DISEASES. 



of the table, and the map or other object to be enlarged is then pinned on a flat 

 board in the right position in front of the lens, the board being held in place by the 



carrier. The desired magnification is obtained by sliding the carrier in or out to a 

 marked place previously determined. 



When not made directh' from the micro- 

 scope, the histological drawings in this book 

 have been made from photographic enlarge- 

 ments. For example, in fig. 72 asolio print 

 or bromide print was made from the photo- 

 micrograph. This was then enlarged three 

 or four times and from the resulting nega- 

 tive a salted-paper silver print or a blue print 

 was made. A drawing was then made on 

 this print with a fine-pointed pen and water- 

 proof India ink. After careful inspection by 

 the writer and such changes as were re- 

 quired to make the drawing correspond more 

 nearh' in all its details to the main lines of 

 the photograph, the brown of the silver, or 

 the blue of the iron salt, was removed by a 

 bath in water containing C)'anide of potash. 

 On reduction by the photoengraver many of 

 the inequalities in the pen-work of such 

 drawings disappear and the pictures closely 

 resemble the originals, whereas if they are 

 drawn without enlargement, and engraved 

 as drawn, the pen lines will in many cases 

 have a more or less ragged appearance. 



*Fic. 133— Top view of the room shown in fig. 132. All of the trays rest on triangular slats 

 covering a deep sink. The screens are raised and lowered very easily by balanced weights. 



-Side view of a small photographic dark-room in Laboratory of Plant Pathology. 



Fig. I34.t 



fFiJ. I34-- 



