CH. IV] CAMBIUM. 63 



Cambium. 



The cambium is a meristematic tissue lying between 

 the xylem and phloem. It is a cell-manufactory, where 

 by cell division new elements are added to the neigh- 

 bouring tissues, viz. xylem and phloem. Thus the new 

 cells which arise in the cambium go to increase the xylem 

 and phloem something in the same way as the meristems 

 at the growing point of the root yield cells for the 

 increment of root and root-cap. 



The cambium will be studied in more detail in the 

 next chapter. In the cambium of the sunflower there is 

 one point of great importance as being introductory to 

 the study of the oak. It will be seen in fig. 23 that in the 

 spaces between the bundles, that is to say, across the 

 primary medullary rays, a tissue is forming precisely like 

 the cambium which lies in the bundle. It finally extends 

 across the medullary ray and joins the cambium of one 

 bundle to that of the next. Thus instead of there being 

 mere strips of cambium running longitudinally down the 

 stem between the xylem and phloem, there comes to be a 

 cylindrical sheath of cambium made up by the coalescence 

 of the cambium of the vascular bundles with the interfas- 

 cicular cambium that arises between the vascular bundles. 



The origin of the interfascicular cambium is physio- 

 logically of interest ; it is due to a kind of rejuvenescence, 

 for the cells which lie between the bundles are mature, 

 and in beginning to divide once more and becoming 

 cambium, they regain as it were the quality of youth. 

 The architectural importance of interfascicular cambium 

 will be considered in the chapter on the oak. It will here 



