142 



Carsten Olsen. 



round the stem. The cambium is rudimental in the fully 

 developed stem, its activity soon ceasing as the whole of 

 the woody tissue is already formed while the stem is quite 

 young. 



The wood consists chiefly of spiral and pitted vessels, 

 tracheids and wood-parenchyma. The vessels are fairly 

 narrow, and in transverse sections, angular; the pitted ves- 

 sels have ringpores, while the wood-parenchyma has single 



J'ig. 7. Cornus suecica. 



Transverse section, showing primary structure of root ; tlie epidermis is dead and partly 

 fallen off; exod, Exodermis; end, Endodermis (Sukkertoppen, Greenland) about "°/,. 



pores; medullary rays are not present, but starch is found 

 in the wood-parenchyma, and inside the latter a medulla 

 with large cells runs in the longitudinal direction of 

 the stem. 



The rhizome (fig. 6) is covered with cork, consisting 

 of rather thickwalled cells and formed sub-epidermally. The 

 bark-cells are arranged rather irregularly inside the cork, 

 they are somewhat thickened collenchymatically and contain 

 starch, which as far as Cornus suecica is concerned, always 



