48 



STRUCTURAL BOTANY 



side by the large-celled cortex, many cells in width 

 (Co), and this again by the single layer of epidermij 

 (Ep). 



FIG. 20. Transverse section through the second internode of 

 the stem of a seedling Wallflower, with seven vascular 

 bundles. Ep, epidermis ; h, hair ; s, stoma ; Co, cortex ; 

 en, endodermis, or innermost layer of cortex ; pc, peri- 

 cycle, or outermost layer of cylinder ; ph, phloem of 

 a vascular bundle ; x, xylem of vascular bundle ; c, cam- 

 bium ; if, medullary ray, or interfascicular tissue ; p t 

 pith. Magnified 55. (R. S.) 



a. The Vascular Bundles 



We will now consider the vascular bundles more in 

 detail, and first we will determine their course as traced 

 longitudinally. Each bundle runs out into a leaf. 

 This fact is most easily proved by tracing the course 

 of the five largest bundles, which correspond in 



