160 METHODS IN PLANT HISTOLOGY 



pulled over a small roller. The "commercial ortho" cut film is very 

 satisfactory; but, as one learns to get the right exposure, the panchro- 

 matic film can be used. Mr. Charles H. Carpenter, the veteran 

 photographer of the Field Museum in Chicago, gave this advice to a 

 beginner: "Pick out a good plate or film, and one developer, and stick 

 to them for the first ten years." 



LANTERN SLIDES 



After securing a good negative, the method of making a lantern 

 slide or paper print depends upon the size of the negative. Slides and 

 paper prints of the same size as the negative are printed by contact. It 

 is hardly worth while to make a lantern slide by enlargement from a 

 tiny negative; the best lantern slides are made by reduction from 

 larger negatives. On the other hand, excellent paper prints can be 

 made by enlargement. 



Lantern slides by contact. — From a 3jX4| negative a lantern shde 

 can be printed by contact, just as one would make a contact print on 

 paper, because the lantern-slide plate (3jx4) is so nearly the size of 

 the negative. If one wants a lantern slide of some feature of a larger 

 negative, the lantern-slide plate can be placed over the desired portion 

 and a contact print can be made. The negative can be placed in a 

 printing frame and the lantern-slide plate placed over it, emulsion side 

 against emulsion side. If the printing frame is larger than the nega- 

 tive, put a piece of clear glass in the frame. If the negative is a glass 

 plate, remember that you are dealing with three thicknesses of glass 

 and do not use too much pressure. 



Hold the frame in the left hand, as far from the bulb as possible, 

 and snap on the light for a second. If the plate is overexposed, use a 

 weaker bulb or increase the distance. If the plate is completely de- 

 veloped within a minute, the exposure was too long. The exposure 

 should be such that full development will require about 1 minute and 

 45 seconds. The prominent features should show clearly when viewed 

 from the back of the slide. 



If the negative is uneven, the distance from the hght may be in- 

 creased so as to lengthen the exposure to several seconds, thus giving 

 time to shade the weak parts. If a negative is harsh and shows too 

 much contrast, hold it closer to the light and shorten the exposure; if 

 weak and lacking in contrast, hold it farther away and lengthen the 

 exposure. 



