STRUCTURE OF STEMS 37 







C. Internal Structure of Herbaceous Exogenous (Dicoty- 

 ledonous) Stems: 



1. Cut some very thin slices of wood and mount one 

 piece in anilin sulphate and one, after it has been 

 moistened with hydrochloric acid, in a solution 

 of phloroglucin (warming the slide, if necessary, to 

 develop the color). What colors are developed in 

 the wood in each of the solutions? (Compare with 

 one in water.) These color reactions are very char- 

 acteristic of lignified (woody) cell-walls, although 

 anilin sulphate also stains some fibers in other than 

 wood regions. 



2. Now cut thin cross-sections of some herbaceous 

 exogenous (dicotyledonous) stem (e.g., garden gera- 

 nium). Mount these sections, some in anilin sul- 

 phate, some in phloroglucin after HC1, and some in 

 water, for microscopic examination. These should 

 show which parts of the herbaceous stem are 

 lignified. Where are these lignified (xylem) por- 

 tions, and how many are there in the stem? Was 

 it easier to cut these or the wood sections? Why? 

 The mass of tissue directly outside of each wood 

 (xylem) region is the phloem tissue of the vascular 

 bundle. Between the xylem and the phloem in each 

 bundle observe a layer of one or two cells of cambium, 

 an actively dividing tissue that produces more xylem 

 and phloem. How are the bundles arranged in the 

 stem? The tissue between the bundles and the 

 periphery of the stem is composed of cortex, covered 

 on the very outside with the epidermis. 



3. Study these sections under the microscope and com- 

 pare them with the corn stem. Do you find t*he 

 same tissues in both cases, or with what exceptions? 

 How do they differ in arrangement? What would 



