92 



VEGETABLE HISTOLOGY. 



Fig. 54. Cross-section of stem of Greenbrier. a, cortex ; b, cylinder sheath, made 

 up of incomplete bundles ; c, a bundle ; d, parenchyma cells of ground tissue 

 (Bastin). 



Fig. 55. Section of a bundle of Greenbrier, magnified, a, large duct in xylem ; b, 

 smaller duct; c, phloem mass; d, parenchyma cell (Bastin). 



OPEN BUNDLES. These are found in stems of dicotyledonous 

 plants. In herbs they are more or less isolated, and the xylem 

 portions do not form a solid continuous woody cylinder, as in 

 shrubs and trees. The cross-section of the Geranium stem fur- 

 nished an example of open collateral bundles. 



To study the bundles in a woody type of stem, make cross- 

 sections of the stem of Bittersweet and stain with phloroglucin. 

 Surrounding a central area of pith cells will be found a thick 

 ring of cells that stain red, composed mainly of thick-walled 

 wood fibres, which are interspersed with cells of much larger 

 diameter, the ducts. This solid ring of cells is composed of the 



