Collecting and Subdividing Plant Materials 7 



loosely in waxed paper. Sporulation continues and may indeed be 

 promoted in this manner. However, since molding and disintegration 

 take place during prolonged storage, material should ])e processed 

 promptly. Small fungi should be wrapped in moist paper, enclosed 

 in waxed paper, and processed as soon as possible. 



PATHOLOGICAL MATERIAL 



Particular care should be exercised to insure that the condition 

 of the host tissues is not altered by handling, in order that abnormal 

 structure may be properly interpreted as an histological symptom of 

 the disease. Prevent wilting of the material, or revive it in a moist 

 chamber, but a\()id the development of bacteria, molds, or other 

 secondary organisms. For a pathological investigation, always collect 

 normal, disease-free tissues of age comparable with the diseased 

 samples. It is imperative to work out the best technique for preserving 

 the "normal" condition of the host before attempting an authoritative 

 interpretation of slides of pathological material. 



The foregoing general remarks will serve as a basis from which 

 the worker can develop effective methods and habits of collecting 

 and handling material in accordance with facilities and circumstances. 

 Hold rigidly to the view that the finished slide should represent the 

 original structure of the plant, whether that structure is presumably 

 normal or pathological or is the result of experimental treatment. 



The handling of materials that are to be used for bulk specimens or 

 whole mounts is described in Chap. 10. The preparation of perma- 

 nent slides from microtome sections consists essentially of the following 

 processes: 



1. Selecting desired plants or parts of plants and, if necessary, subdividing 

 into suitable pieces. 



2. The killing and preservation of the contents of cells and the preserva- 

 tion of cellular structures in a condition approximating that in the living 

 plant. 



3. Embedding in a matrix if necessary, in order to support the tissues for 

 sectioning. See page 91 for the sectioning of unembedded tissues. 



4. Sectioning of the tissues into very thin slices. 



5. Staining the slices and covering with a cemented cover glass to make 

 a permanent slide. 



Subdividing Material for Processing 



Some preliminary remarks concerning the action of reagents in 

 the preservation of cells and tissues will aid in understanding the 

 following description of this process. The reagents used for killing 



