46 
ness of the mounts renders reéxamination under the microscope 
distinctly unsatisfactory and in some cases impossible. 
The technique of the Canada balsam, Venetian turpentine, 
glycerine and glycerine jelly methods of mounting is so well known 
that discussion is hardly necessary. With Canada balsam the 
material must be dehydrated and then passed through different 
grades of xylol before mounting, involving a distinct time ele- 
ment. Another objection, other than the time involved, is that 
very delicate thin structures frequently contract and curl. With 
Venetian turpentine there is less curling and little shrinkage, the 
chief objection here being the tedious technique. Glycerine and 
glycerine jelly preparations are particularly unsatisfactory, as they 
cannot be filed with the herbarium specimens, and moreover they 
cannot be considered as permanent mounts. 
For all ordinary purposes in connection with herbarium prac- 
tice the best medium so far tested is ordinary water glass (sodium 
silicate). The manipulation of this medium is simple in the 
extreme. Sodium silicate can be used direct with either boiled 
or fresh material and either in the field or in the laboratory. The 
parts of dried specimens selected for examination are boiled in 
water until they are soft and can be readily dissected without 
breaking. After dissection and study the extra water on the slide 
is removed by applying the edge of a piece of blotting paper. 
The dissections are then properly arranged and allowed to dry 
slightly in the air, after which a little sodium silicate is droppe 
on the slide, the amount being in proportion to the dissected 
material to be preserved. Sodium silicate solidifies quickly, hence 
it is essential that the cover glass be added with little delay. In 
Practice, ordinary glass slides have been found to be most satis- 
factory, but mica, isinglass, or thin celluloid may also be used. 
The great advantage of this method is that the finished slide 
may be placed almost at once in a packet attached to the sheet, 
which is distinctly advantageous as compared with the more com- 
mon method of preserving them in cabinets, remote from the her- 
barium specimens with which they logically belong. The pre- 
pared slides are permanent, dry, easy to use, and there is com- 
paratively little shrinkage or distortion of the dissectons. While 
sr method is not adapted to finer phases of microscopic techmqu® 
it 1s admirably adapted to ordinary herbarium purposes. 
With fresh material the technique is much the same as with 
