15 



PLATE VIII. 



HISTOLOGY OF PLOWEEING- PLANT. 



STEM 



DIAG. 1 . TRANSVERSE SECTION of a one-year-old stem of Horse Chestnut 

 Pitli or medulla in centre. 



Fibro-vascular bundles arranged in a riug round the pith 

 Wood or xylem, including medullary sheath. 

 Cambium, a soft cellular layer. 

 Bast or phloem outside the cambium. 

 Cortex, connected with the pith by the medullary rays. 

 Epidermis. 



Note, The part of the stem outside the soft cambium is readily removable, and is the separable bark. 



Fio. 1. TRANSVERSE SECTION of same stem under the microscope 

 Pith, consisting of parenchyma cells. 

 Fibro-vascular bundle 

 Wood or xylem 



Vessels, large openings. 

 Wood-cells between the vessels. 

 Cambium, small thin-walled cells. 

 Bast or phloem 



Soft portion, made up of thin-walled cells. 



Hard portion, or liber layer, made up of round thick-walled cells, the central cavity 



being almost obliterated. 



Medullary rays, brick-shaped cells between the fibro-vascular bundles. 

 Cortex, angular cells, parenchyma. 

 Epidermis, a single layer of squarish cells. 

 FIG. 2. LONG. SECTION of the Horse Chestnut stem 

 Pith-cells. 



Fibro-vascular bundle 

 Wood- 

 Spiral vessels of medullary sheath, elongated tubes with spirally thickened walls. 

 Annular vessels, elongated tubes with ringlike thickenings. 

 Dotted ducts, elongated tubes thickened so as to leave thin places, the dots. 

 Wood-cells, elongated, and when older with thick walls, and then called woody 



fibres or wood prosenchyma. 

 Cambium, thin-walled cells. 

 Bast- 

 Soft bast, elongated thin-walled cells. 



Hard bast, thick-walled and elongated cells forming the flexible bast fibres. 

 Cortex, parenchymatous cells. 

 Epidermis, a single layer of cells. 



FIGS. 3, 4. SECTIONS of stem of Butcher's Broom magnified 

 Differences from Horse Chestnut stem 



Fibro-vascular bundles are not arranged in a ring round pith, but scattered irregu- 

 larly. 

 No cambium and therefore no provision for increase after first year. 



