138 Botanical Microtechnique 



The desirability of using choice sections showing the bark in three 

 planes cannot be overemphasized. In addition to serving as supple- 

 mentary class material for studying the structure and development of 

 the stem, such preparations serve as reference material for research, 

 especially for pathological studies. Even in wood technology, in w^hich 

 the work is largely confined to the microscopic structure of the ^\ood, 

 preparations showing the cambium, phloem, cortex, and periderm are 

 a valuable supplement. 



Seasoned lumber is frequently used as a source of material for 

 slides, and excellent preparations can be made from such material. 

 However, parenchymatous elements such as xylem parenchyma and 

 the epithelial cells of resin canals are collapsed and distorted. The 

 preparations are adequate for diagnostic purposes and for the study 

 of nonliving elements of the xylem. For best results, use properly 

 seasoned wood and prepare the blocks so that sections can be cut 

 accurately along the three conventional planes as described in 

 Chap. 2. The specialized sectioning methods necessary for dry or 

 hard -woods are described on ))ages 84-85. 



The Root 



The processing of roots of seed plants lor anatomical study is 

 similar to the methods used for stems. The meristematic root tip is 

 usually prepared by careful cytological methods; sections max then be 

 stained either with a cytological stain for nuclear struct ines or stained 

 with some histological (ombination. Batches of rcjot tips that do not 

 have abundant mitotic figures are usually set aside for histological 

 preparations. The methods of obtaining root tips are described in 



Chap. 9. 



1 lu' histogens of roots are evident at the root ti]), especially if the 

 preparation is stained to show cell walls as xvcll as nuclei. Ihe 

 primary tissues are evident at the beginning of the root-hair zone, 

 where the emerging root hairs can be delected \viih a hand lens. 

 Initiation of lateral root primordia can be demonstrated at tlie upper 

 limits of the root-hair /one. wluie the old tool haiis arc beginning to 

 collapse. At this icxcl tlie j)rimary tissues are usually clearly 

 differentiated, without being excessively woody. 



Favorable subjects h)i ilhisii atiiig the monocot root are maize and 

 /is JHiitii^iis i)fii< inali.s. [Uv garden asparagus. Germinate corn ni 



Fir,. 13.10— fl. Transverse section of root of Aspnrni^ii.s ofjirinalis showing initiation of 



laicra! root: /', i)racc root of Zca. 



