io PRACTICAL BOTANY 



never apply a reagent at haphazard, but only when you have a 

 definite purpose for doing so. 



These rules apply specially to staining reagents, which 

 should only be used when their assistance is actually required : 

 the primary end of the anatomical investigations detailed 

 below is not to prepare a number of objects pleasing to the 

 uneducated eye, but to gain a knowledge of the structure of 

 the plant-body as it is in the living state, and this end may as 

 a rule be best attained by the simplest methods. 



2. See that the glass slide and the cover-glass are perfectly 

 clean and dry, and show a bright polished surface before using 

 them ; they should be cleaned immediately before use, and, 

 after cleaning, their surfaces should not be touched with the 

 fingers, nor should the cover-glass be laid flat on the table, but 

 tilted on its edge. 



3. In mounting, whatever the fluid may be, take only so 

 small a drop of it as shall just suffice to fill the space between 

 the slide and the cover-glass, and extend to the margin of the 

 cover: judgment as to the quantity necessary can only be 

 acquired by practice. If too much fluid has been used the 

 excess must be soaked up with slips of blotting-paper, or filter 

 paper. 



4. The practice of scrupulous cleanliness cannot be too strongly 

 impressed upon students as the basis of all successful work with 

 the microscope, and it is in the use of fluid reagents that the 

 greatest care is necessary ; if too large a quantity be used it 

 is apt to extend to the lower surface of the slide, and so to the 

 stage of the microscope : or to be smeared over the upper side 

 of the cover- slip, and may then gain access even to the ob- 

 jective ; it is absolutely necessary that both the front lens of the 

 objective, and the upper side of the cover-slip be perfectly clean 

 and dry, also the lower surface of the slide and the stage of the 

 microscope, ,-" 



5. Having taken a sufficiently small drop of the mounting 

 medium, and having placed the object in it, bring down the cover-, 

 glass obliquely upon the drop so that one edge of it is first wette^ 

 by the medium, then let down the slip gently, so as to allow the 

 medium time to spread out under the cover-slip ; this may be 



