148 FLOWERING PLANTS 
held between the thumb and forefinger of the left hand; its 
edge should just touch the slide at the outer limit of the water, 
and then by means of a needle it is gently lowered, being thus 
gradually wetted, the water at the same time spreading out into 
the thinnest layer possible. In this way air-bubbles are avoided, 
whereas if the cover-glass is simply dropped down, it is difficult to 
see anything clearly on account of the air-bubbles. It takes a little — 
practice to put down cover-glasses well. : 
If it is desired to stain the organisms in the drop of water te: 42), 
it is best to do so after the cover-glass has been put on. A small 
strip of blotting-paper is placed against the left-hand side of the 
cover-glass ; a drop of stain (iodine is often used) is taken up on a 
glass rod and applied to the opposite edge of the cover-glass. The 
blotting-paper (or filter-paper) sucks up some of the water, thus 
creating a current, and the stain is drawn in. 
If the object to be examined under the microscope is several 
layers of cells thick, such as a stem or leaf, a section must be cut. 
. If the substance is hard, as a stem, it can be held firmly in the left 
hand. The surface is cut as smoothly as possible, and with a sharp 
razor a very thin slice is made. It takes considerable practice, in 
cutting sections, to get very thin, even slices. When even, the 
section lies flat on the slide, but if uneven, it will not be flat, the 
cover-glass will not lie evenly on it, and it will not be possible to 
examine it with a high power. In cutting sections, the blade of the 
razor must be kept wet, and it should be drawn towards the person, 
not in the opposite direction ; it should be kept as flat as possible. 
When the section that is being cut is really thin, it is possible to 
see the colour of the steel as the razor is drawn through the 
substance. 
If a thin substance like a leaf is to be cut, it must be put 
between something solid. The pith of elder is generally used ;-a 
piece of carrot will do. The leaf is put between two pieces of pith 
or carrot. A thin section is cut of the pith or carrot, and the leaf is’ 
cut at the same time. 
Sections are often stained in order to bring out the outlines of 
the cells more clearly. For this purpose some aniline dye, such as 
gentian blue or methyl violet, is. often used. (There are special 
stains for special purposes; thus the structure of a sieve-plate is 
best brought out by eosin.) Two or three drops of the stain are 
put into a watch-glass containing water. The solution should be 
faint rather than dark-coloured, as too deep staining of a section 
conceals instead of making the cells clearer. The section is placed 
