144 



Carsten Olsen. 



The bark consists of rather large cells ; the epidermis 

 dies away very quickly, and remains as a loose sheath round 

 the very young root, while the exodermis, the cells being 

 yet well filled with protoplasm, soon produces a layer ot 

 corky tissue with thickened cells, and resembles otherwise 

 the cork of the rhizome. 



The secondary root (fig. 8) is on the whole of the same 



Fig. 9. Cornus suecica. 



Tangential, longitudinal section tlirough the bark of a young root, containing mycorrhizae; 

 a, destroyed hyphae (Greenland) about ""/i. 



structure as the rhizome, the exception being that no me- 

 dulla is found. 



Endotrophic mycorrhiza is always found in the young 

 root, in Arctic as well as in Danish specimens (fig. 9); the 

 fungal hyphae are rather thick and not very closely knotted 

 together, as is most often the case with roots having endo- 

 trophic hyphae. The hyphae are both inter- and intracel- 

 lular, and in the cells are also found irregular or coral-shaped 

 clumps, probably destroyed hyphae, which like the former 



