102 PHOTO-MICROGRAPHS. 
deeply colored septate spores referred to. They 
may be dusted upon the surface of a slide and 
photographed, dry, without the use of a cover- 
glass, or they may be mounted in an aqueous 
medium, or in glycerine, in a very shallow cell. 
The latter method gives the best results. 
To get rid of air-bubbles, which will give great 
trouble if the attempt is made to introduce the 
spores at once into water or glycerine, it is best 
first to wet them thoroughly with alcohol, and 
before this has entirely evaporated, to place them 
in the medium which has been selected. 
A good plan is to place a drop of alcohol in the 
centre of a glass slide, and to bring in contact 
with it a patch of mould in full fruit. The spores 
will be detached upon contact with the alcohol, 
and will sink to the bottom of the drop. By a 
little agitation of the slide they will be distributed 
in a tolerably uniform layer upon the surface of 
the glass. When they are nearly dry, in conse- 
quence of the evaporation of the alcohol, this is 
replaced by a drop of distilled water, or of glycer- 
ine, and the thin glass cover is applied. The 
superfluous fluid is removed with blotting-paper 
(Swedish filtering-paper is the best), and a circle 
of zinc cement may be turned around the edge of 
the glass to prevent evaporation while the ex- 
posure is being made, or if the intention is to 
preserve the preparation. A circle of cement is 
not used to support the margin of the glass cover, 
as the aim should be to have as thin a stratum of 
fluid as possible, in order to prevent the spores 
