CHAPTER I 



GENERAL DIRECTIONS AS TO THE PREPARATION 



OF MATERIAL AND THE VALUE OF 



PARTICULAR SECTIONS 



In determining the course to be followed in the preparation of 

 material and its subsequent study, it is impossible to too strongly 

 emphasize the fact that a correct and complete conception of the 

 details of structure embraced in the vascular cylinder of the stem 

 can be obtained only when the latter is studied from three points 

 of view, or in three planes of section, - - the transverse, the radial, 

 and the tangential, the last two of which are of necessity also 

 longitudinal. Although the importance of these three planes of 

 section is well recognized by scientific botanists, it seems desirable 

 to restate the fact in order to avoid any misconception which 

 might otherwise arise through the minor importance attached to 

 the longitudinal sections by recent authors (79, 350). Under cer- 

 tain circumstances it sometimes happens that all three planes of 

 section are not available, and the student is then compelled to 

 rely upon two points of view or possibly even one for his con- 

 clusions. In such an extremity it becomes possible to draw 

 deductions from the material in hand as to the aspects of the 

 structure presented by the remaining plane or planes of section, 

 and so to reconstruct with approximate accuracy the entire 

 fabric. But such a method should never be resorted to except 

 when absolutely necessary, since to employ it under other cir- 

 cumstances would involve a measure of doubt which would bring 

 justifiable discredit upon the conclusions reached. The relative 

 value of each section for such purposes will appear shortly. 



In proceeding to the study of a given wood too much stress 

 cannot be placed upon the importance of very searching and accu- 

 rate observations, especially if one is about to draw a diagnosis 



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