91 ELEMENTARY TISSUES. 



3. Occasional Ducts (long tubes marked with bordered pits, 

 bands, etc.) 



4. Rectangular cells of medullary rays, if present. To Avhat 

 tissue-form do tbey belong? 



In the transection: 



OBSERVE: 1. Ends of wood-cells in very regular radial rows ; 

 thickness of their walls, etc. 



2. The larger openings (ducts), marking each years growth. 



3. Thin plates of medullary tissue. 



4. The bark with ends of bast appearing. 



5. Pith at center. 



Bastin, p. 159 ; Goodale, pp. 88, 89. 



Notice the brittleness of wood, and strength of bast, corres- 

 ponding to the difference in the length of cells in each. 



Usually wood-cells are less regularly distributed than in the 

 above. 



PREPARATION for (a), (b), (c), and (d). Make a radial longitudi- 

 nal section (i. e., a longitudinal section passing the center of the pith). 

 Around the pith is a sheath of Spiral or Reticulated vessels (see 

 Type 1). In the woody tissue of the section are Pitted vessels 

 (see Type 2). 



OBSERVE : 1. The Spiral Ducts. 



2. That the spiral appearance is due to the thickened //<///<- 

 deposited on the inner surface of a thin-walled tube. 



3. If there are any Reticulated or Annular vessels in the 

 medullary sheath. 



4. That the Pitted vessels are furnished with "bordered pits" 

 the outline of the pit or cavity being nearly circular, and the 

 "lumen" or central aperture oblong. 



Vines' Text Book of Bot., p. 134; Goodale, p. 85; Bessey, p. 

 74; Strasburger, p. 129. 



V. Tracheary Tissue (continued). 



Illustration : Sections of the stems of CURRANT, HORSE 

 CHESTNUT, MOON SEED and GRAPE VINES, are to be mounted to serve as 

 material for the study of both Tracheids and Ti-(t<-li. Note 

 carefully the distinction between the two, the former being ' /!/>< 

 wood cells in outline >nl ///> I V.W/N < Tr<ic/n <i< in xtrnct nr<il 

 ma rkings.' 1 ' 1 Read carefully DeBary, pp. 1G4-1G6. 



