Bulletin - United States National Museum - Smithsonian Institution

FLORA OF WASHINGTON AND VICINITY. 221
How long should plants remain in press? Never over twenty -four
hours for the first time, and certain plants will suffer if left in so long.
3Iuch, however, depends upon the pressure. Those who press their
plants hard must change them oftener. .
If the above suggestions are
followed, it is best to change the driers at the end of twelve hours.
The second time they may in most cases be allowed to remain in twenty-
four hours ; after this they should be changed every day for about four
days. The jjressure may be slightly increased after each change, and
after the fourth it is usually safe and advisable to leave them in the
press two days, then change and leave in two dajs more, under hard
pressure, after which they may be taken out, the driers renewed, and
the package laid aside for a week, with merely a board or a book upon it,
to dry out. The plants will then be ready for the herbarium.
The process of changing the driers is more simjile than that of press-
ing. The press is placed upon the table before you, a little to the right ;
the upper press board is taken oft' and placed, cleats downward, on the
table by the side of it, at the left ; the package of dry brown paper lies
on the left of these. A layer of these latter is placed on the empty
press-board as in the case of pressing the plants; the upper layer of
damp ones is taken from the package and laid by the side of it, at the
right (a table at least five feet long is required) ; then the top specimen
in its two sheets of white paper is carefully taken off, without disturb-
ing the plant, and placed on the layer of dry papers. A new layer of
dry papers is then placed over these, the second layer of wet ones re-
moved from the package, and the second plant transferred in the same
manner as before to the new package. This process is continued until
all the plants are transferred from wet to dry pajjers. No amount of
curiosity should tempt you to remove the upper white paper to look at
a specimen. After a plant ha^ been placed between thin papers it should
never again be in the least disturbed until it is fully dry. The access
of the air and the separation of the leaves and flowers from the inti-
mate contact which pressure gives them with the thin sheets deadens the
lively color which the plants otherwise will preserve, and injures the
specimens. The thin paper is no perceptible obstruction to the passage
of the moisture from the plant to the driers. Some, instead of using
two sheets, use one folded double sheet, but this makes the process of
manipulation more difQcult, without any corresponding advantage. The
object in having tliem white and a little larger than the driers is to
avoid overlooking them ; if smaller than the driers, one is constantly