16 Methods in Plant Histology 



the box. For ordinary class work, slides of medium thickness are 

 more serviceable, but for critical cytological work many investigators 

 prefer very thin slides. 



There is never any objection to very thin covers, except that they 

 require care in cleaning. For mounts which are to be used with an 

 immersion lens, it is better to have the cover of the same width as 

 the slide. The advantage is evident, since there is no danger of 

 getting balsam on the cover when wiping off the immersion fluid; 

 besides, one can put sections to the very edge of the slide and still 

 be sure that they will be covered. Since most mounts for research 

 work are mounted under long covers and are intended for examina- 

 tion with immersion lenses, we should recommend covers of 25X50 

 mm., or even 25X60 mm. Round covers are desirable only when 

 mounts are to be sealed on a turntable. Larger slides and corre- 

 spondingly larger covers are needed for special purposes. 



By consulting a catalog, which will be furnished by any dealer, 

 the beginner can determine what he needs to buy, and what he can 

 find substitutes for, if it is necessary to be very economical. 



