INTRODUCTION 



N THE WORK carried out by the United States Department of 



Agriculture on the development of improved methods for preparing 



specimens of agricultural material, it was found that the procedures 



outlined below are practicable within certain limitations for the classes 



of material defined for each. 



The two preservation methods described in this manual are: 



1. Preservation of plant specimens by chemical treatment to retain 

 their natural color and, after dehydration, mounting them in two- 

 dimensional form in plastic plates. This method is applicable, with 

 suitable modifications, to flowers, leaves, roots, and such other plant 

 parts as lend themselves to being mounted in a flattened condition. 



2. Embedment of three-dimensional specimens of biological material 

 in blocks of transparent plastic. This method is limited to specimens 

 that can be dehydrated without undesirable change in form or color 

 and are not altered in appearance by the action of the plastic during 

 embedding. 



Each of these two preservation methods is designed to produce only 

 the particular type of mount described, and is limited in application to 

 the classes of material specified. In selecting the method to be em- 

 ployed for preserving and mounting a given specimen, it is important, 

 therefore, to make sure that it is capable of being processed in the 

 manner desired and that the resulting mount is of the type that will 

 be suitable for the intended use. 



The application of these methods should be undertaken only by 

 persons who have a working knowledge of biology and chemistry, or 

 who are under the guidance or supervision of adequately informed 

 individuals. 



It is not practicable in a publication of this kind to warn the readers 

 against all dangers to be anticipated in variations of the processes out- 

 lined. General cautions are included in part 2, beginning on page 32 

 and continuing on pages 33, 34, 36, and 38; others are scattered through- 

 out the manual. Different conditions or the use of different compounds 

 and combinations might introduce additional hazards. 



The subject matter contained in this publication is based mainly on 

 the development work on specimen preservation carried out in the 

 United States Department of Agriculture. Consideration has, how- 

 ever, also been given to the published results of other workers in the 

 field, and the publications consulted are listed at the end of this manual. 



In the development of the methods here described cooperation was 

 received from numerous agencies and individuals, including the Bureau 

 of Plant Industry, Soils, and Agricultural Engineering; the Bureau of 

 Entomology and Plant Quarantine; the Forest Service; the Extension 

 Service; the National Herbarium and other divisions of the Department 

 of Biology of the Smithsonian Institution; the National Bureau of 

 Standards; the botany departments of the George Washington Uni- 

 versity and the University of Pennsylvania; the New York Botanical 

 Garden; the Brooklyn Botanic Garden; the Philadelphia Academy of 

 Natural Sciences; the Arnold Arboretum and the Gray Herbarium of 

 Harvard University; the Wildflower Preservation Society; and the New 

 England Herb Society. 



During the compilation of these instructions the subject matter was 



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