18 MISC. PUBLICATION 679, U. S. DEPT. OF AGRICULTURE 



Curing specimen material after it has been laid out.— Plant material 

 that has been pressed and dried before treatment, in the manner de- 

 scribed in this section, may be cured at room temperatures of 24° C. 

 (approximately 75° F.) or less if the relative humidity is not higher than 

 60 percent. At higher room temperatures or under more humid condi- 

 tions, the curing should be carried out under refrigeration at a relative 

 humidity of between -±0 and 60 percent. Xo well defined indications 

 are observable to serve as a guide in determining when specimens 

 processed in this manner are fully cured, but it has been found that a 

 period of 3 to 5 days, depending upon the thickness and the permeability 

 of the specimen, is usually adequate. 



At the end of the curing period, the specimen should be examined 

 to make sure that it has remained in proper arrangement and is free 

 from objectionable bubbles. It is not necessary to remove all the bub- 

 bles in the preserving fluid around the specimen at this time, because 

 they can generally be taken care of more easily when the protecting 

 cover film is finally removed after dehydration has been completed; 

 but all bubbles directly over or under the specimen should be eliminated 

 before proceeding with the dehydration step. In cases where it is found 

 necessary to rework the layout for the purpose of removing bubbles or 

 rearranging parts of the specimen, the partially dried preserving fluid 

 should first be completely softened again by remoistening the layout 

 under a pad of wet newspapers for at least 20 minutes. 



When the specimen has been properly arranged and freed from 

 bubbles, the overlapping waxed paper marginal pockets should be cut 

 off, and the extruded preserving fluid in them may be either reused or 

 discarded. The paper on the back of the Vinylite mounting sheet 

 should now be removed, and the exposed surface of the sheet cleaned 

 with wet paper pads and dried with soft tissue or cloth. 



Procedure B — Treating Fresh Specimens With Preserving Fluid 



Under Film 



When the natural colors cannot be satisfactorily retained through the 

 pressing and drying process or when it is difficult to arrange the material 

 in the press, or the material is not suitable for treating in a bath, the 

 processing in most cases can be carried out by this second procedure. 

 This consists in laying out the specimen while it is still in a fresh state 

 and then processing it in the same general manner as under procedure A, 

 except that the curing is carried out under refrigeration. 



This procedure is mainly applicable to specimens that are made up of 

 thin parts, and is especially suitable for plants that have finely divided 

 leaves or complex inflorescences or root systems that are difficult to 

 handle either by pressing or by the immersion method. It may. how- 

 ever, be applied if desired to various other types of material in which 

 relatively thin tissues prevail. 



Laying out the specimen and applying the preserving fluid. — The 

 specimen should be cleaned thoroughly to make sure that all gritty 

 material that might puncture the cover film is eliminated. The lower 

 mounting plate, which consists of a 0.030-inch thick sheet of transparent 

 Vinylite plastic, large enough to provide a space of at least 1 inch all 

 around the specimen, should be prepared with protective tissue and 

 waxed paper backing as directed for procedure A. and a temporary 



