108 THE MICROSCOPE. July 



PRACTICAL SUGGESTIONS. 



By L. a. WILLSON, 

 cleveland, ohio. 



Puccinias, — This form of fung-us is now rapidly ripening-. 

 They comprise something- over a hundred species. 

 They are known as mildews or brands and attack and 

 are found g-rowing- on a g-reat variety of plants. 



It is a matter of commercial importance to identify them 

 and destroy them as they work havoc with crops of 

 cereals and other valuable plants. No two species have 

 spores alike; in this respect they rival diatoms for the mi- 

 croscopic student ; besides they need no cleaning- or mani- 

 pulation. Finding an infected plant, scrape a little of a 

 pustule, with a spatula, transfer to a drop of water on a 

 slide, cover and examine with a quarter objective. If you 

 are acquainted with this fung-us purchase a lot of speci- 

 mens from a dealer in microscopical supplies ; most deal- 

 ers have packages containing- forty or fifty specimens 

 which are sold very reasonably. Some of the spores are 

 very beautiful. 



Spot Lens and Paraboloid Illuminator Effects. — Near- 

 ly all the beauties of a spot lens or a paraboloid illuminator 

 can be obtained by the use of oblique illuminator with a 

 low power. Butterfly scales, scales of synapta, pollen 

 g-rains and in fact nearly all objects may be beautifully 

 exhibited by oblique illumination. This effect is well ac- 

 complished by turning- the mirror aside from the axis of 

 the microscope. 



Arsenic. — The microscope is often an indispensable 

 aid, in some of the tests for arsenic. The most common 

 form of the crystal is octohedial or tetrahechol, but a right 

 rombic form may be obtained by sublimation. Protoxide 

 of antimony will also yield by sublimation similar cr3'stals. 

 The crystals may be seen with the microscope to the lU,. 

 000 of a g-rain. In Marsh's test metalic arsenic is formed 

 in the upper part of the test tube, which may be examined 

 under the microscope. Sulphuretted hydrog-en precipi- 



