TIIE SEEDLING AND YOUNG PLANT. 67 



cambium. The radial rows of the latter can be followed 

 for some distance, the radial diameter of the cells in- 

 creasing, the walls thickening, and the rectangular shape 

 changing. Displacements from the radial arrangement 

 then occur. A few cells assume a nearly circular form 

 (i. e., in transverse section), and the larger ones are ef- 

 fective in causing displacements. The bast cells devel- 

 oped earlier, and therefore more distant from the cam- 

 bium zone, now lie in the perceptibly large periphery, 

 and thus undergo tangential extension or radial com- 

 pression, and so undergo changes of form. Besides these 

 alterations in form and position, the more delicate bast 

 elements increase in numbers by the development of 

 perpendicular division Avails ; this is quite clear in those 

 parts nearest the cambium, but farther out, where great 

 irregularity occurs, it is impossible to say which cells 

 have arisen direct from the cambium and which by these 

 later divisions. Still, certain thin septa betray their late 

 origin. 



On tangential sections we see elongated, pointed, in- 

 terpectinating cells, with secondary rays of parenchyma 

 between, showing that these are formed and continued 

 by the cambium. Each pointed cell has proceeded from 

 a cambium cell, and indeed only differs in its thicker 

 walls and pits. These cells are still simple, or here and 

 there have a transverse septum obliquely across. If the 

 tangential section is in a slightly older portion, most of 

 the above cells are found to be septate and cut up into 

 parenchyma-like cells irregular bast-parenchyma. The 



