THE VASCULAR TISSUES. 



73 



Subsidiary tissues occurring in the Central Cylinder of Dicoty- 

 ledonous and Coniferous Stems and Roots. 

 These are : — 



i. The endodermis or Stareh-Sheath (occurring in both stem 



and root), 

 ii. The pSFieycle (roots only). This tissue is meristematic. 



iii. The medulla or pith, with its medullary sheath. 



i. The endodermis, bun die -sheath, or starch-sheath is a ring 

 of cells, only one cell thick, which marks the limits of the central 

 cylinder in a stem or root of more than one year's growth 

 (Dicotyledons, Coniferfe).* Its component cells at times contain 



Fig. 56. — Endodermis Cells in a Longitudinal Section uf the young 

 Stem op Coryhus avellana (Hazel). — c, Endodermal cells with starch- 

 granules (stained with iodine) ; 6, bast-fibres ; c, cortical cells. 



starch-granules, and in many cases a distinctive feature is the 



presence of peculiar fusiform thickenings on their radial walls. 



Functionally this layer forms a starch reservoir, but in many 



■* The separate bundles or schizosteles in the rhizomes of certain Pterido- 

 phyta (Pteris) are also surrounded by an endodermis. 



