10 Knud Jessen. 



derm being formed — the latter contains small intercellular 

 spaces — and a secondary woody part. The most vigorous 

 roots in my Greenland material had just begun the develop- 

 ment of these structures, but the cortex was living and con- 

 tained a large amount of starch especially in the part within 

 the exodermis. 



In the cortex of the absorbent roots from Greenland 

 fungal hyphæ occurred; these are also recorded by Freiden- 

 felt in plants from Sweden. 



The creeping stem is distinguished anatomically from the 

 floral shoot, partly by its secondary formations and partly 

 by the fact that normally bast is absent from it. 



The epidermis of the year's shoot is rather small-celled, 

 the outer wall is about 4.5^ thick; and the outermost layer 

 of the cortex is slightly collenchymatous. The cortex, in the 

 middle, consists of especially large cells, some of which die 

 at an early period, forming large lacunæ separated by radiat- 

 ing trabecular. The cortex of the floral stem behaves in 

 the same manner. During the first period of vegetation the 

 cortex of the shoot dies, but it is found attached to the shoot 

 even during the third year. The central cylinder is surround- 

 ed by an endodermis. In the floral shoot the several-layered 

 pericycle is transformed into bast tissue, and only in one 

 particular case did I find bast in the rest of the shoot also, 

 viz. in a plant which grew among shrubs and whose annual 

 shoots of the three last years protruded about y 2 metre verti- 

 cally above the surface of the bog. 



The periderm is formed in the outermost layer of the 

 pericycle, and even in the first period of vegetation it reaches 

 a thickness of several layers. Moreover it appears to be 

 stronger in Arctic specimens, and while in Denmark, at any 

 rate when young, it probably does not contain cork-cells, in 

 the material from Greenland 1 — 2 layers of phelloid-cells 

 alternated with one layer of cork-cells, and as many as 6 



