226 PLANT ANATOMY. 
system, consists almost entirely of cubical or horizontally (radi- 
ally) extended (parellelopipedal), thin-walled cells which are 
joined together in a wall-like form, without intervening spaces 
(ames et se [ee | em 
Oooo macy 
Fig. 143.—Wall-like cells of the medullary rays from Lignwm Juniperi, ona radial 
longitudinal section. 
(Fig. 143). This regularity is lost at the place where the me- 
dullary rays pass into the bark. 
a 
mm 
a L) 
‘ 
Cena nod 5 ) 
Loto . 4 eX: Cie bE 
a fe Se ere: 3 Mg a ee 
i 
i.” 
Fie. 144.—Single-rowed medullary rays, r, in Stipes Dulcamare, which gradually be- 
come lost in the bark ; i, inner bark ; m, middle bark; a, outer bark (Berg). 
- In the cambial zone, when the growth in thickness is already 
