28 



VEGETABLE PHYSIOLOGY 



found in the cortex. The stem of Juncus shows these 

 two forms combined together. 



Still more complicated cases show sclerenchyma arising 

 in all three regions, sometimes the bands being all 

 independent, sometimes united in various ways. In 

 Cladium Mariscus those of all the regions are united into 

 a continuous system which goes from the tegumentary 



FIG. 31. -VASCULAR BUNDLE OF STEM OF MONOCOTYLEDONOUS PLANT. 

 (After Kny.) 



pit, phloem ; x, xylem vessels ; p ph, protophloem. The bundle 

 is surrounded by a small-celled sheath of sclerenchyma. 



region towards the interior of the stem, embracing the 

 vascular bundles and attaching them to each other. 



Similar differentiation of the supporting system is found 

 in many leaves, in which it subserves the same purposes. 

 In many cases the veins afford sufficient protection against 

 tearing or rupture in consequence of violent winds. The 

 methods of their arrangement in many cases subserve 



