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 



