164 METHODS IN PLANT HISTOLOGY 



5X7 negative, in good daylight, with an F16 stop, try 2 or 3 seconds. 

 If enlarging from a negative somewhat smaller than a lantern slide, 

 try 8 or 10 seconds. Other things being equal, the best lantern slides 

 are made by reduction from larger negatives and the poorest, by en- 

 largement from smaller negatives. 



The superiority of the larger negative is easily demonstrated. With 

 a 5X7 camera, make a negative of some elaborately ornamented 

 building, making the building just cover the plate. Then with a vest- 

 pocket camera, or even a 2jX3|, make a similar negative, so that the 

 building just covers the plate. Make lantern slides from both nega- 

 tives, so that the building is of the same size on both lantern slides. 

 While the building, as it appears on the screen, is of the same size, no 

 matter which slide is used, the one from the larger negative will show 

 finer detail. The same is true for all kinds of plant subjects. Small 

 cameras are easy to carry and their small films are cheap, but they 

 have no other recommendation. A 3iX4|, with a high grade 4.5 

 anastigmatic lens, is good, even for scientific work; but a 5X7 is better. 

 If you are strong and ambitious or have some one to carry the heavy 

 load, take an 8X 10. 



Staining lantern slides. — Some of the stains used in staining mi- 

 croscope slides will give a pleasant tone to lantern slides. Light green 

 gives a clear, moonlight effect. Phloxine gives a transparent, rosy tint. 

 Sepia and other tones could doubtless be imitated by this easy method. 



Clearing lantern slides. — Sometimes a slide will seem perfectly 

 clear, just as it comes from the fixing bath, especially from an acid fixing 

 bath; usually, however, it will be better to transfer the slide from the 

 fixing bath to a weak solution of acetic acid — just enough acid to give 

 the solution the taste of weak vinegar — and then rock for a minute 

 before washing. 



The following clearing fluid may be used in the same way : 



Metric Apothecaries' 



Alum 20 g. (1.3 gr.) 



Iron sulphate 20 g. (1.3 gr.) 



Citric acid 20 g. (1.3 gr.) 



Water 500 c.c. (17 oz.) 



Coating lantern slides. — After the slide has become thoroughly dry, 

 a coat of balsam or shellac will add much to its brilliancy. Dilute the 

 Canada balsam with xylol until it becomes almost as thin as water; 

 balance the slide on the thumb and first, second, and third fingers. 



