Metaphyta L ilium. 151 



character of the tissues present, but in their arrangement. 

 It is easy to make out the fibro-vascular strands grouped 

 together and forming a perfect cylinder in the centre, and 

 surrounded by the vascular sheath or layer of fundamental 

 tissue next to the cylinder. Outside the fibro-vascular 

 cylinder is a very thick cortex (fig. 69). The epidermis 

 soon disappears, and its place is taken by the outer layers 



FIG. 69. TRANSVERSE SECTION- ROOT OF Acorus calamus. (Sachs.) 



PP 



s, fibro-vascular sheath, surrounded by cortical parenchyma and external to 

 the pericambium ; pp, xylem ; ph, phloem ; g, g, p, p, vessels of xylem. 



of the cortex. Within the sheath, we again find points of 

 difference from the stem in the arrangement of the various 

 parts of the strands themselves. Immediately internal to 

 the vascular sheath is a layer of cells known as the peri- 

 cambium, or phloem-sheath, which encloses the strands. 

 The bast and wood of the strand, however, are not arranged 



