Betts. — Roiiette Flanis at Cass. 



267 



Leaf -base (fig. 22). — The leaf-base is elongated and sheathing, colour- 

 less, and thickened considerably near the centre, but thin and membranous 



Fig. 22. — Plantago triandra. Transverse section of petiole ( x 48). 

 a, aqueous tissue ; b, xylem ; c, phloem ; d, bundle-sheath. 



atjthe margins. The upper epidermis consists of large,fthin-walled, colour- 

 less cells, without any stomata. The outer walls are slightly thicker than 

 the others. The lower epidermis is composed of smaller cells than the 

 upper, and the walls are somewhat thicker. 



The ground-tissue consists of large, rounded, thin-walled cells in which 

 the protoplasm is reduced to a very thin layer lining the walls ; this tissue 

 is for water-storage. The vascular bundles are small, and of the same 

 structure as in the leaf. 



Fig. 23. — Plantago triandra. Transverse section of root (x 175) 

 a, suberized cells ; 6, cortex ; c, endodermis ; d, peri- 

 cycle ; e, phloem ; /, xylem. 



'Root (fig. 23). — The vascular cylinder is small, consisting of a central 

 mass of xylem, composed of elements of smaU diameter, and with thickened, 

 pitted walls ; surrounding the xylem is a narrow band of phloem. The 

 pericycle is a single layer of thin-walled cells. The endodermis is well 

 marked, and consists of cells somewhat larger than the cells of the peri- 

 cycle and with thicker, slightly suberized walls. 



