84 BACTERIAL DISEASES OF PLANTS 



10"; cost $57) but without success, since the temperature proved 

 too variable. 



Stains and Staining Jars. A full set of Griibler's stains 

 are very desirable. Few persons know how to use any great 

 number of them, but for those few who do they should be avail- 

 able. It is best to buy them in unbroken packages. We use 

 the Coplin staining jar (figured in " Bacteria in Relation to Plant 

 Diseases," Vol. I, p. 121). There is nothing better than this. 



Mounting Media. This varies, of course, with the nature of 

 the sections. I have not fallen in love with glycerine or glycer- 

 ine jelly mounts, but as made by some persons they appear to be 

 quite permanent. We employ mostly Canada balsam or Dam- 

 mar balsam. It should be purchased only from makers of the 

 highest reputation, e.g., Griibler, with special reference to free- 

 dom from traces of acids which, if present, will infallibly bleach 

 and ruin the best stained slides in course of time. I formerly 

 made my own balsam, of good quality, by purchasing the best 

 grade of crude balsam and driving off all volatile products in 

 an oven kept for some days at the proper temperature, after 

 which the brittle unburned residue was dissolved in xylol to 

 the proper consistency. I was forced to do this by inability 

 to find at that time any fit balsam on the market. 



Microscopes. When properly stained, mounted and dry, 

 the sections are ready for study. For this purpose only the best 

 microscopes are recommended. At least the objectives, eye- 

 pieces, and the substage apparatus should be of the very best 

 workmanship, owing to the small size of the objects sought 

 and the need of studying them in a clear light with very sharp 

 definition. The fine adjustment also should have a very slow 

 movement. 



The writer now uses only the Carl Zeiss instruments and 

 specially recommends his photomicrographic stand, but the one 

 shown in Fig. 55 rather than the newer pattern which is very in- 

 convenient to carry, having only two separate awkward finger 

 holes in place of the convenient large opening on the old pattern. 

 It is also less well finished, e.g., in the two which we have, the 

 vernier plate at the right projects above the stage and catches 

 the end of the slide, making it very inconvenient to use with 



