CHAPTER V. 



THE SEEDLING AND YOUNG PLANT (continued}. 



STRUCTURE OF THE VASCULAR TISSUES, ETC. 



BEFORE plunging into the intricacies of the vascu- 

 lar bundles it will be well to obtain some idea of the 

 general plan of structure which they present on trans- 

 verse section (Fig. 9). As already seen, each of the 

 bundles of the ring consists of a xylem portion on the 

 side next the center of the stem, and a phloem portion 

 on the side next the periphery, and these portions are 

 separated by the cambium layer. The tissue in the 

 center of the stem, and surrounded by the ring of bun- 

 dles, is called the pith ; the tissue outside the ring, and 

 between it and the epidermis, is called the cortex ; and 

 the tissue left between the bundles is termed the pri- 

 mary medullary rays (Fig. 9). 



It will, of course, be remembered that the term 

 " ring," as used above, always expresses the fact that a 

 cylinder is here viewed in section. Now, the cambium 

 of the individual bundles soon unites across the primary 

 meflullary rays, and thus a complete hollow cylinder of 

 cambium is formed throughout the stem, and, as we 

 shall see later, throughout the root also. For the pres- 



