328 PRACTICAL BOTANY 



pressed parts of the channels, while it is reduced on 

 the sloping sides of the ridges to the single layer of 

 thick-walled epidermal cells. 



iii. Beneath this is a broad band of cortical tissue, 

 in which may be recognized 



a. Groups of chlorophyll-parenchyma of oval 

 outline : one of these lies on each slope of the furrows, 

 and extends to points close below the surface of the 

 sloping sides. 



b. Parenchyma composed of rounded cells with little 

 or no chlorophyll. 



c. Large intercellular cavities, which alternate 

 in position with the ridges, and are thus opposite the 

 channels of the outer surface. 



iv. The cortex is limited internally by a single 

 sinuous layer consisting of cells in close contact with 

 one another : this is the endodermis : it forms a 

 continuous and sinuous ring surrounding 



v. The vascular bundles, which may be recog- 

 nized as oval groups of elements of smaller size than 

 those of the surrounding tissue : they alternate in 

 position with the intercellular cavities of the cortex, 

 and are thus opposite to the ridges which project on 

 the external surface. 



vi. The pith, which lies centrally, consists of thin- 

 walled tissue, and is in great part obliterated by a 

 large central cavity. 



III. Before proceeding to the more minute study of 

 these several tissues, cut transverse sections through a 

 leaf-sheath : mount in glycerine, and examine with a 

 low power. It may be observed that the arrangement 

 of tissues is not unlike that of the peripheral tissues 



