APPENDIX 



The following brief notes on certain phases of microtechnique 

 are given here to facilitate the use of this book by the teacher and 

 student. For full information on the various procedures used 

 in preparing tissue for microscopic study, reference should be 

 made to the publications of Chamberlain (1932), Rawlins (1933), 

 Johansen (1940), and Sass (1940), cited under "General 

 References. ' ' 



Free-hand Sections 



In many of the exercises in this book, directions are given for 

 the study of sections cut by hand from living stems, leaves or 

 other plant structures. To prepare such material requires only 

 simple technique and in addition provides a realistic picture of 

 cells and tissues which should precede the examination of micro- 

 tomed and permanently-stained preparations. In the laboratory 

 the student can acquire the necessary skill with a sectioning- 

 razor to enable him to explore the structure of such tissues as the 

 epidermis, parenchyma and collenchyma. Sections cut by hand 

 should be carefully mounted on a clean slide either in distilled 

 water or in the various reagents designated and the cover-glass 

 lowered gently into place. For more resistant cells, such as 

 sclereides or fibers and for the critical study of the sieve-plates 

 in phloem elements, the nse of the carbon dioxide freezing micro- 

 tome is highly desirable. With the aid of this instrument, a large 

 number of thin sections may be jirepared by the instructor in 

 advance of class use. The student must learn to check free-hand 

 preparations at frequent intervals so that the sections are not 

 allowed to dry out. Cells immersed in fluid are not only easier 

 to study from an optical point of view but they also retain a 

 more or less normal structure over a relatively long period of 

 observation. Sections of hairy objects, such as many leaves or 

 stems, are often dii^icult to mount in water without the formation 

 of numerous air-bubbles. This difficulty may be removed by 



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