THE SEEDLING AND YOUNG PLANT 67 
chiefly of delicate, apparently irregular parenchyma 
cells with cellulose walls; this is easily traced to the 
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 effec- 
tive in causing displacements. The bast-cells developed 
earlier, and therefore more distant from the cambium 
zone, now lie in the perceptibly larger periphery, and 
thus undergo tangential extension or radial compression, 
and so undergo changes of form. Besides these altera- 
tions in formand position, the more delicate bast elements 
increase in numbers by the development of perpendicular 
division walls; this is quite clear in those parts nearest 
the cambium, but further out, where great irregu- 
larity 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, 
interpectinating cells, with secondary raysof parenchyma 
between, showing that these are formed and continued 
by the cambium. Lach pointed cell has proceeded from 
acambium 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 
F 2 
