I02 



PLANT ORGANS OR PARTS OF PLANTS. 



Histology. — In the branches a periderm surrounds the 

 thick, yellowish cortex. A cambium line separates this 

 from the thin and angular medullary portion. The bark 

 is radially striated by convoluted bast-fibres and wedge- 

 shaped medullary rays, and the wood by similar woody 

 and medullary rays. The main trunk has the same 

 appearance, except that the medullary portion is missing. 



The periderm consists of flat cork-cells in layers, the 



Fig. 17. — Longitudinal Section of Glycyrrhiza. 

 g, Pitted and reticulated vessels, tracheids to left; Kr, crystal sac; 

 bast fibres; hp, wood parenchyma. 



primary bark of few rows of starch-containing parenchyma 

 cells. The inner bark is much broader and is made up of 

 three- to- seven rowed medullary rays and wedge-shaped 

 bast-fibres. The cells of the medullary rays are tangen- 

 tially elongated, thin-walled, and filled with starch. 

 The chief mass of the bast rays consists of parenchyma 

 cells with rounded bundles of thickened bast-fibres. The 

 separate bast-fibres have quite a considerable length, and 



