lid. Introduction 



The presentation of detailed directions for specific subjects must 

 be prefaced by certain reservations and precautions. Reactions of 

 plants vary with their age, degree of differentiation, degree of turgor, 

 and perhaps many intangible physiological factors. Each step in the 

 processing in\olves a time factor, the duration of that particular 

 treatment. The numerous successive operations, each with a variable 

 time factor, offer innumerable combinations of treatment. This is 

 complicated by variations in the purity of reagents, fluctuations of 

 room temperature, failure of oven thermostats, and just plain blunders 

 by the worker. The possibilities of influencing the finished product 

 are obvious. Therefore the author of a research paper or a manual 

 is reluctant to present a set of written directions with any assurance 

 of success to his readers. However, a study of the general principles of 

 collecting, killing, and processing, as outlined in Chaps. 1, 2, and 3, 

 will enable the reader to use the following directions with reasonable 

 assurance of success. 



This section of the manual should be regarded as closely linked 

 with Part I. The general methods of collecting and processing de- 

 scribed in Part I will now be supplemented by specific recommenda- 

 tions as to suitable plants for illustrating various topics and the tech- 

 niques of processing these plants. The reader should refer back fre- 

 quently to pertinent portions of Part I. 



Plants selected for study not only should show the desired struc- 

 tural features to best advantage but also should have the virtue of 

 familiarity to the student and availability. Why use Vanilla, a rare 

 orchid, to illustrate the anatomy of the monocot root when the 

 common garden asparagus yields instructive slides? Some of the slides 

 used for teaching should be of species other than those illustrated in 

 the official textbook. This demands more critical study of the slides 

 by the students and minimizes the copying of text figures. The plants 



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