CHAPTER XII 



SPECIAL METHODS 



It has been the object of the preceding chapters to give the student 

 an introduction to the principal methods of preparing plant material 

 for microscopic study, and to afford him such a grounding in funda- 

 mentals that he will be able to develop methods which may be neces- 

 sary in special cases. 



A few methods designed to meet special difficulties are given in this 

 chapter and others are mentioned in the second part of the book, in 

 connection with various laboratory types. 



VERY LARGE SECTIONS 



It is sometimes desirable to cut very large sections. Sections as 

 large as a cornstalk may be cut freehand, but cut better when im- 

 bedded in paraffin or celloidin. Even when cutting a paraffin section 

 of a corn stem, have the knife somewhat oblique, and if the section 

 shows a tendency to curl, as it probably will, a gentle touch with the 

 finger will prevent the curling. If the knife, for the best cutting, is too 

 oblique for ribbons, take each section off separately and put it in a box. 



A section of a stem of Zamia 5 or 6 cm. in diameter is difficult to 

 handle by the usual methods. If a large microtome, such as is used in 

 cutting complete sections of large brains, is available, the piece of 

 stem is easily held for the cutting. Some of the medium-sized sliding 

 microtomes now have a rigid clamp which will grip a block 3 cm. 

 square. The lower part of the piece can then be trimmed to fit the 

 clamp, leaving the upper part round, so that sections across a stem 6 

 or 7 cm. in diameter may be cut without much difficulty. With a 

 rather soft stem, like Zamia, the surface must be flooded with 95 per 

 cent alcohol after each section, if it is desirable to cut thin sections. 

 From stems 3 cm. in diameter, sections can be cut at about 20 to 30 /x. 

 If the section is not more than 3 or 4 cm. in diameter, it can be mount- 

 ed on a 50X75 mm. sHde. Sections 6 or 7 cm. in diameter can be 

 mounted on lantern slides; if large covers are not available, use another 

 lantern slide for a cover. It will be easier to get neat mounts if the 

 cover is cut down so as to leave a margin 2 or 3 mm. wide. It is not 



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