286 



Methods in Plant Histology 



of potash is a good filter, if the preparation has been stained in violet. 

 Similarly, various filters may be used according to the staining of the 

 more critical structures. 



The Welsbach lamp furnishes an excellent light. It should be 

 placed so that the rays will be focused upon the mirror of the micro- 

 scope. Some of the more powerful acetylene bicycle lamps are quite 



FIG. 105. A wash bottle used as a condenser 



satisfactory. The Argand type of gaslight is good, but will usually 

 need a reflector behind it. A kerosene lamp must also be reinforced 

 by a reflector. The old-fashioned silvered reflector, still used in 

 country churches and halls, will do, but is hardly equal to the cheap 

 reflectors of shorter focus which are so commonly used with incandes- 

 cent electric lights. The incandescent electric light itself has not 

 given satisfactory results. Small electric arc lights, tempered with 

 ground glass and filters, are very satisfactory; the only objection is 



